Muscle targeting complexes and uses thereof for treating facioscapulohumeral muscular dystrophy

ABSTRACT

Aspects of the disclosure relate to complexes comprising a muscle-targeting agent covalently linked to a molecular payload. In some embodiments, the muscle-targeting agent specifically binds to an internalizing cell surface receptor on muscle cells. In some embodiments, the molecular payload inhibits expression or activity of DUX4. In some embodiments, the molecular payload is an oligonucleotide, such as an antisense oligonucleotide or RNAi oligonucleotide.

RELATED APPLICATION

This application claims priority under 35 U.S.C. § 119(e) to U.S.Provisional Patent Application No. 63/220,155, filed Jul. 9, 2021,entitled “MUSCLE TARGETING COMPLEXES AND USES THEREOF FOR TREATINGFACIOSCAPULOHUMERAL MUSCULAR DYSTROPHY,” which is hereby incorporated byreference in its entirety.

FIELD OF THE INVENTION

The present application relates to targeting complexes for deliveringmolecular payloads (e.g., oligonucleotides) to cells and uses thereof,particularly uses relating to treatment of disease.

REFERENCE TO AN ELECTRONIC SEQUENCE LISTING

The contents of the electronic sequence listing(D082470069US01-SEQ-ZJG.xml; Size: 205,257 bytes; and Date of Creation:Jul. 1, 2022) is herein incorporated by reference in its entirety.

BACKGROUND OF INVENTION

Muscular dystrophies (MDs) are a group of diseases characterized by theprogressive weakness and loss of muscle mass. These diseases are causedby mutations in genes which encode proteins needed to form healthymuscle tissue. Facioscapulohumeral muscular dystrophy (FSHD) is adominantly inherited type of MD which primarily affects muscles of theface, shoulder blades, and upper arms. Other symptoms of FSHD includeabdominal muscle weakness, retinal abnormalities, hearing loss, andjoint pain and inflammation. FSHD is the most prevalent of the ninetypes of MD affecting both adults and children, with a worldwideincidence of about 1 in 8,300 people. FSHD is caused by aberrantproduction of double homeobox 4 (DUX4), a protein whose function isunknown. The DUX4 gene, which encodes the DUX4 protein, is located inthe D4Z4 repeat region on chromosome 4 and is typically expressed onlyin fetal development, after which it is repressed by hypermethylation ofthe D4Z4 repeats which surround and compact the DUX4 gene. Two types ofFSHD, Type 1 and Type 2 have been described. Type 1, which accounts forabout 95% of cases, is associated with deletions of D4Z4 repeats onchromosome 4. Unaffected individuals generally have more than 10 repeatsarrayed in the subtelomeric region of chromosome 4, whereas the mostcommon form of FSHD (FSHD1) is caused by a contraction of the array tofewer than 10 repeats, associated with decreased epigenetic repressionand variegated expression of DUX4 in skeletal muscle. Two allelicvariants of chromosome 4q (4qA and 4qB) exist in the region distal toD4Z4. 4qA is in cis with a functional polyadenylation consensus site.Contractions on 4qA alleles are pathogenic because the DUX4 transcriptis polyadenylated and translated into stable protein. Type 2 FSHD, whichaccounts for about 5% of cases, is associated with mutations of theSMCHD1 gene on chromosome 18. Besides supportive care and treatments toaddress the symptoms of the disease, there are no effective therapiesfor FSHD.

SUMMARY OF INVENTION

According to some aspects, the disclosure provides complexes that targetmuscle cells for purposes of delivering molecular payloads to thosecells. In some embodiments, complexes provided herein are particularlyuseful for delivering molecular payloads that inhibit the expression oractivity of DUX4, e.g., in a subject having or suspected of havingFacioscapulohumeral muscular dystrophy (FSHD). Accordingly, in someembodiments, complexes provided herein comprise muscle-targeting agents(e.g., muscle targeting antibodies) that specifically bind to receptorson the surface of muscle cells for purposes of delivering molecularpayloads to the muscle cells. In some embodiments, the complexes aretaken up into the cells via a receptor mediated internalization,following which the molecular payload may be released to perform afunction inside the cells. For example, complexes engineered to deliveroligonucleotides may release the oligonucleotides such that theoligonucleotides can inhibit DUX4 gene expression in the muscle cells.In some embodiments, the oligonucleotides are released by endosomalcleavage of covalent linkers connecting oligonucleotides andmuscle-targeting agents of the complexes.

One aspect of the present disclosure relates to a complex comprising ananti-transferrin receptor (TfR) antibody covalently linked to amolecular payload configured for reducing expression or activity ofDUX4, wherein the antibody comprises:

(i) a heavy chain variable region (VH) comprising an amino acid sequenceat least 95% identical to SEQ ID NO: 76; and/or a light chain variableregion (VL) comprising an amino acid sequence at least 95% identical toSEQ ID NO: 75;

(ii) a heavy chain variable region (VH) comprising an amino acidsequence at least 95% identical to SEQ ID NO: 69; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 95%identical to SEQ ID NO: 70;

(iii) a heavy chain variable region (VH) comprising an amino acidsequence at least 95% identical to SEQ ID NO: 71; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 95%identical to SEQ ID NO: 70;

(iv) a heavy chain variable region (VH) comprising an amino acidsequence at least 95% identical to SEQ ID NO: 72; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 95%identical to SEQ ID NO: 70;

(v) a heavy chain variable region (VH) comprising an amino acid sequenceat least 95% identical to SEQ ID NO: 73; and/or a light chain variableregion (VL) comprising an amino acid sequence at least 95% identical toSEQ ID NO: 74;

(vi) a heavy chain variable region (VH) comprising an amino acidsequence at least 95% identical to SEQ ID NO: 73; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 95%identical to SEQ ID NO: 75;

(vii) a heavy chain variable region (VH) comprising an amino acidsequence at least 95% identical to SEQ ID NO: 76; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 95%identical to SEQ ID NO: 74;

(viii) a heavy chain variable region (VH) comprising an amino acidsequence at least 95% identical to SEQ ID NO: 77; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 95%identical to SEQ ID NO: 78;

(ix) a heavy chain variable region (VH) comprising an amino acidsequence at least 95% identical to SEQ ID NO: 79; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 95%identical to SEQ ID NO: 80; or

(x) a heavy chain variable region (VH) comprising an amino acid sequenceat least 95% identical to SEQ ID NO: 77; and/or a light chain variableregion (VL) comprising an amino acid sequence at least 95% identical toSEQ ID NO: 80.

In some embodiments, the antibody comprises:

(i) a VH comprising the amino acid sequence of SEQ ID NO: 76 and a VLcomprising the amino acid sequence of SEQ ID NO: 75;

(ii) a VH comprising the amino acid sequence of SEQ ID NO: 69 and a VLcomprising the amino acid sequence of SEQ ID NO: 70;

(iii) a VH comprising the amino acid sequence of SEQ ID NO: 71 and a VLcomprising the amino acid sequence of SEQ ID NO: 70;

(iv) a VH comprising the amino acid sequence of SEQ ID NO: 72 and a VLcomprising the amino acid sequence of SEQ ID NO: 70;

(v) a VH comprising the amino acid sequence of SEQ ID NO: 73 and a VLcomprising the amino acid sequence of SEQ ID NO: 74;

(vi) a VH comprising the amino acid sequence of SEQ ID NO: 73 and a VLcomprising the amino acid sequence of SEQ ID NO: 75;

(vii) a VH comprising the amino acid sequence of SEQ ID NO: 76 and a VLcomprising the amino acid sequence of SEQ ID NO: 74;

(viii) a VH comprising the amino acid sequence of SEQ ID NO: 77 and a VLcomprising the amino acid sequence of SEQ ID NO: 78;

(ix) a VH comprising the amino acid sequence of SEQ ID NO: 79 and a VLcomprising the amino acid sequence of SEQ ID NO: 80; or

(x) a VH comprising the amino acid sequence of SEQ ID NO: 77 and a VLcomprising the amino acid sequence of SEQ ID NO: 80.

In some embodiments, the antibody is selected from the group consistingof a Fab fragment, a Fab′ fragment, a F(ab′)2 fragment, a scFv, a Fv,and a full-length IgG. In some embodiments, the antibody is a Fabfragment.

In some embodiments, the antibody comprises:

(i) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 101; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 90;

(ii) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 97; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 85;

(iii) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 98; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 85;

(iv) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 99; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 85;

(v) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 100; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 89;

(vi) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 100; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 90;

(vii) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 101; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 89;

(viii) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 102; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 93;

(ix) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 103; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 95; or

(x) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 102; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 95.

In some embodiments, the antibody comprises:

(i) a heavy chain comprising the amino acid sequence of SEQ ID NO: 101;and a light chain comprising the amino acid sequence of SEQ ID NO: 90;

(ii) a heavy chain comprising the amino acid sequence of SEQ ID NO: 97;and a light chain comprising the amino acid sequence of SEQ ID NO: 85;

(iii) a heavy chain comprising the amino acid sequence of SEQ ID NO: 98;and a light chain comprising the amino acid sequence of SEQ ID NO: 85;

(iv) a heavy chain comprising the amino acid sequence of SEQ ID NO: 99;and a light chain comprising the amino acid sequence of SEQ ID NO: 85;

(v) a heavy chain comprising the amino acid sequence of SEQ ID NO: 100;and a light chain comprising the amino acid sequence of SEQ ID NO: 89;

(vi) a heavy chain comprising the amino acid sequence of SEQ ID NO: 100;and a light chain comprising the amino acid sequence of SEQ ID NO: 90;

(vii) a heavy chain comprising the amino acid sequence of SEQ ID NO:101; and a light chain comprising the amino acid sequence of SEQ ID NO:89;

(viii) a heavy chain comprising the amino acid sequence of SEQ ID NO:102; and a light chain comprising the amino acid sequence of SEQ ID NO:93;

(ix) a heavy chain comprising the amino acid sequence of SEQ ID NO: 103;and a light chain comprising the amino acid sequence of SEQ ID NO: 95;or

(x) a heavy chain comprising the amino acid sequence of SEQ ID NO: 102;and a light chain comprising the amino acid sequence of SEQ ID NO: 95.

In some embodiments, the antibody does not specifically bind to thetransferrin binding site of the transferrin receptor and/or wherein theantibody does not inhibit binding of transferrin to the transferrinreceptor. In some embodiments, the antibody is cross-reactive withextracellular epitopes of two or more of a human, non-human primate androdent transferrin receptor. In some embodiments, the complex isconfigured to promote transferrin receptor mediated internalization ofthe molecular payload into a muscle cell.

In some embodiments, the molecular payload is an oligonucleotide. Insome embodiments, the oligonucleotide comprises an antisense strandcomprising a region of complementarity to a DUX4 RNA. In someembodiments, the oligonucleotide comprises an antisense strandcomprising a region of complementarity to a non-coding region of theDUX4 RNA. In some embodiments, the oligonucleotide comprises anantisense strand comprising a region of complementarity to a 5′ or 3′UTR of the DUX4 RNA.

In some embodiments, the antisense strand comprises at least 15consecutive nucleotides of SEQ ID NO: 151 (GGGCATTTTAATATATCTCTGAACT).

In some embodiments, the antisense strand comprises the nucleotidesequence of SEQ ID NO: 151 (GGGCATTTTAATATATCTCTGAACT).

In some embodiments, the oligonucleotide further comprises a sensestrand that hybridizes to the antisense strand to form a double strandedsiRNA. In some embodiments, the oligonucleotide comprises at least onemodified internucleoside linkage. In some embodiments, theoligonucleotide comprises one or more modified nucleosides. In someembodiments, the one or more modified nucleosides are 2′-modifiednucleosides. In some embodiments, the oligonucleotide is aphosphorodiamidate morpholino oligomer.

In some embodiments, the antibody is covalently linked to the molecularpayload via a cleavable linker. In some embodiments, the cleavablelinker comprises a valine-citrulline sequence.

In some embodiments, the antibody is covalently linked to the molecularpayload via conjugation to a lysine residue or a cysteine residue of theantibody.

In some embodiments, reducing expression or activity of DUX4 comprisesreducing DUX4 RNA levels. In some embodiments, reducing expression oractivity of DUX4 comprises reducing DUX4 protein levels.

Another aspect of the present disclosure relates to a method of reducingDUX4 expression or activity in a cell, the method comprising contactingthe cell with the complex in an effective amount for promotinginternalization of the molecular payload in the cell, optionally whereinthe cell is a muscle cell.

Another aspect of the present disclosure relates to a method of treatinga subject having one or more deletions of a D4Z4 repeat in chromosome 4that is associated with facioscapulohumeral muscular dystrophy, themethod comprising administering to the subject an effective amount ofthe complex.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a non-limiting schematic showing the effect oftransfecting cells with an siRNA.

FIG. 2 depicts a non-limiting schematic showing the activity of a muscletargeting complex comprising an siRNA.

FIGS. 3A-3B depict non-limiting schematics showing the activity of amuscle targeting complex comprising an siRNA in mouse muscle tissues(gastrocnemius and heart) in vivo, relative to vehicle-treated controls.(N=4 C57BL/6 WT mice)

FIGS. 4A-4E depict non-limiting schematics showing the tissueselectivity of a muscle targeting complex comprising an siRNA.

FIG. 5 depicts a non-limiting schematic showing the expression levels ofDUX4 in three DUX4-expressing cell lines (A549, U-2 OS, and HepG2 celllines) and immortalized skeletal muscle myoblasts (SkMC).

FIG. 6 depicts non-limiting schematics showing the ability of aphosphorodiamidate morpholino oligomer (PMO) version of an antisenseoligonucleotide that targets DUX4 (FM10 PMO) to reduce expression levelsof downstream DUX4 genes (ZSCAN4, MBD3L2, TRIM43).

FIG. 7 depicts a non-limiting schematic showing the ability of amuscle-targeting complex (anti-TfR antibody-FM10) comprising ananti-TfR1 Fab (RI7 217) conjugated to FM10 antisense oligonucleotide toreduce expression levels of downstream DUX4 genes (ZSCAN4, MBD3L2,TRIM43) in human U-2 OS cells, relative to naked FM10 antisenseoligonucleotide.

FIG. 8 shows the serum stability of the linker used for linking ananti-TfR antibody and a molecular payload (e.g., an oligonucleotide) invarious species over time after intravenous administration.

FIGS. 9A-9F show binding of humanized anti-TfR Fabs to human TfR1(hTfR1) or cynomolgus monkey TfR1 (cTfR1), as measured by ELISA. FIG. 9Ashows binding of humanized 3M12 variants to hTfR1. FIG. 9B shows bindingof humanized 3M12 variants to cTfR1. FIG. 9C shows binding of humanized3A4 variants to hTfR1. FIG. 9D shows binding of humanized 3A4 variantsto cTfR1. FIG. 9E shows binding of humanized 5H12 variants to hTfR1.FIG. 9F shows binding of humanized 5H12 variants to hTfR1.

FIG. 10 shows the quantified cellular uptake of anti-TfR Fab conjugatesinto rhabdomyosarcoma (RD) cells. The molecular payload in the testedconjugates are DMPK-targeting oligonucleotides and the uptake of theconjugates were facilitated by indicated anti-TfR Fabs. Conjugateshaving a negative control Fab (anti-mouse TfR) or a positive control Fab(anti-human TfR1) are also included this assay. Cells were incubatedwith indicated conjugate at a concentration of 100 nM for 4 hours.Cellular uptake was measured by mean Cypher5e fluorescence.

FIGS. 11A-11F show binding of oligonucleotide-conjugated or unconjugatedhumanized anti-TfR Fabs to human TfR1 (hTfR1) and cynomolgus monkey TfR1(cTfR1), as measured by ELISA. FIG. 11A shows the binding of humanized3M12 variants alone or in conjugates with a DMPK targeting oligo tohTfR1. FIG. 11B shows the binding of humanized 3M12 variants alone or inconjugates with a DMPK targeting oligo to cTfR1. FIG. 11C shows thebinding of humanized 3A4 variants alone or in conjugates with a DMPKtargeting oligo to hTfR1. FIG. 11D shows the binding of humanized 3A4variants alone or in conjugates with a DMPK targeting oligo to cTfR1.FIG. 11E shows the binding of humanized 5H12 variants alone or inconjugates with a DMPK targeting oligo to hTfR1. FIG. 11F shows thebinding of humanized 5H12 variants alone or in conjugates with a DMPKtargeting oligo to cTfR1. The respective EC50 values are also shown.

FIG. 12 shows DMPK expression in RD cells treated with variousconcentrations of conjugates containing the indicated humanized anti-TfRantibodies conjugated to a DMPK-targeting oligonucleotide AS0300. Theduration of treatment was 3 days. The AS0300 was delivered usingtransfection agents were used as control.

FIGS. 13A-13B show expression of MBD3L2, TRIM43, and ZSCAN4 transcriptsin FSHD patient-derived myotubes treated with naked FM10 (FIG. 13A) orFM10 conjugated to anti-TfR1 (FIG. 13B) over a range of concentrations.

FIG. 14 shows ELISA measurements of binding of anti-TfR Fab 3M12 VH4/Vk3to recombinant human (circles), cynomolgus monkey (squares), mouse(upward triangles), or rat (downward triangles) TfR1 protein, at a rangeof concentrations from 230 pM to 500 nM of the Fab. Measurement resultsshow that the anti-TfR Fab is reactive with human and cynomolgus monkeyTfR1. Binding was not observed to mouse or rat recombinant TfR1. Data isshown as relative fluorescent units normalized to baseline.

FIG. 15 shows results of an ELISA testing the affinity of anti-TfR Fab3M12 VH4/Vk3 to recombinant human TfR1 or TfR2 over a range ofconcentrations from 230 pM to 500 nM of Fab. The data are presented asrelative fluorescence units normalized to baseline. The resultsdemonstrate that the Fab does not bind recombinant human TfR2.

FIG. 16 shows the serum stability of the linker used for linkinganti-TfR Fab 3M12 VH4/Vk3 to a control antisense oligonucleotide over 72hours incubation in PBS or in rat, mouse, cynomolgus monkey or humanserum.

FIG. 17 shows that conjugates containing an anti-TfR Fab 3M12 VH4/Vk3conjugated to a DUX4-targeting oligonucleotide (SEQ ID NO: 151)inhibited DUX4 transcriptome in C6 (AB1080) immortalized FSHD1 cells, asindicated by decreased mRNA expression of MDB3L2, TRIM43, and ZSCAN4.The conjugates showed superior activities relative to the unconjugatedDUX4-targeting oligonucleotide in inhibiting DUX4 transcriptome.

FIGS. 18A-18B show dose response curves for gene knockdown. FIG. 18Ashows MBD3L2 knockdown in C6 (AB1080) immortalized FSHD1 cells treatedwith conjugates containing an anti-TfR Fab 3M12 VH4/Vk3 conjugated to aDUX4-targeting oligonucleotide (SEQ ID NO: 151). FIG. 18B shows MBD3L2,TRIM43, and ZSCAN4 knockdown in FSHD patient myotubes treated withconjugates containing an anti-TfR Fab 3M12 VH4/Vk3 conjugated to aDUX4-targeting oligonucleotide (SEQ ID NO: 151). FIG. 18B includes theMBD3L2 data shown in FIG. 18A.

FIG. 19 shows non-human primate plasma levels of DUX4-targetingoligonucleotide (SEQ ID NO: 151) over time following administration of30 mg/kg unconjugated (‘naked’) oligonucleotide or 3, 10, or 30 mg/kgoligonucleotide equivalent of conjugates comprising anti-TfR1 Fab 3M12VH4/Vk3 covalently linked to the DUX4-targeting oligonucleotide(‘Fab-oligonucleotide conjugate’).

FIG. 20 shows tissue levels of DUX4-targeting oligonucleotide (SEQ IDNO: 151) measured in non-human primate muscle tissue samples two-weeksfollowing administration of 30 mg/kg unconjugated (‘naked’)oligonucleotide or 3, 10, or 30 mg/kg oligonucleotide equivalent ofconjugates comprising anti-TfR1 Fab 3M12 VH4/Vk3 covalently linked tothe DUX4-targeting oligonucleotide (‘Fab-Oligonucleotide conjugate’).

FIG. 21 shows tissue levels of DUX4-targeting oligonucleotide (SEQ IDNO: 151) measured in non-human primate muscle tissue samples collectedby biopsy one-week following administration (left 5 bars) or by necropsytwo-weeks following administration (right 5 bars) of 30 mg/kgunconjugated oligonucleotide (‘Oligo’) or 3, 10, or 30 mg/kgoligonucleotide equivalent of conjugates comprising anti-TfR1 Fab 3M12VH4/Vk3 covalently linked to the DUX4-targeting oligonucleotide(‘Conjugate’).

DETAILED DESCRIPTION OF INVENTION

Aspects of the disclosure relate to a recognition that while certainmolecular payloads (e.g., oligonucleotides, peptides, small molecules)can have beneficial effects in muscle cells, it has proven challengingto effectively target such cells. As described herein, the presentdisclosure provides complexes comprising muscle-targeting agentscovalently linked to molecular payloads in order to overcome suchchallenges. In some embodiments, the complexes are particularly usefulfor delivering molecular payloads that inhibit the expression oractivity of target genes in muscle cells, e.g., in a subject having orsuspected of having a rare muscle disease. For example, in someembodiments, complexes are provided for targeting a DUX4 to treatsubjects having FSHD. In some embodiments, complexes provided hereincomprise oligonucleotides that inhibit expression of DUX4 in a subjectthat has one or more D4Z4 repeat deletions on chromosome 4. In someembodiments, complexes provided herein comprise molecular payloads suchas guide molecules (e.g., guide RNAs) that are capable of targetingnucleic acid programmable nucleases (e.g., Cas9) to a DUX4 gene in orderto inactivate the gene in muscle cells, for example, by removing aportion of the DUX4 gene, or by introducing an inactivating mutation orstop codon into the DUX4 gene. In some embodiments, such nucleicprogrammable nucleases could be used to inactivate DUX4 that isaberrantly expressed in muscle cells.

Further aspects of the disclosure, including a description of definedterms, are provided below.

I. Definitions

Administering: As used herein, the terms “administering” or“administration” means to provide a complex to a subject in a mannerthat is physiologically and/or (e.g., and) pharmacologically useful(e.g., to treat a condition in the subject).

Approximately: As used herein, the term “approximately” or “about,” asapplied to one or more values of interest, refers to a value that issimilar to a stated reference value. In certain embodiments, the term“approximately” or “about” refers to a range of values that fall within15%, 14%, 13%, 12%, 11%, 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, orless in either direction (greater than or less than) of the statedreference value unless otherwise stated or otherwise evident from thecontext (except where such number would exceed 100% of a possiblevalue).

Antibody: As used herein, the term “antibody” refers to a polypeptidethat includes at least one immunoglobulin variable domain or at leastone antigenic determinant, e.g., paratope that specifically binds to anantigen. In some embodiments, an antibody is a full-length antibody. Insome embodiments, an antibody is a chimeric antibody. In someembodiments, an antibody is a humanized antibody. However, in someembodiments, an antibody is a Fab fragment, a Fab′ fragment, a F(ab′)2fragment, a Fv fragment or a scFv fragment. In some embodiments, anantibody is a nanobody derived from a camelid antibody or a nanobodyderived from shark antibody. In some embodiments, an antibody is adiabody. In some embodiments, an antibody comprises a framework having ahuman germline sequence. In another embodiment, an antibody comprises aheavy chain constant domain selected from the group consisting of IgG,IgG1, IgG2, IgG2A, IgG2B, IgG2C, IgG3, IgG4, IgA1, IgA2, IgD, IgM, andIgE constant domains. In some embodiments, an antibody comprises a heavy(H) chain variable region (abbreviated herein as VH), and/or (e.g., and)a light (L) chain variable region (abbreviated herein as VL). In someembodiments, an antibody comprises a constant domain, e.g., an Fcregion. An immunoglobulin constant domain refers to a heavy or lightchain constant domain. Human IgG heavy chain and light chain constantdomain amino acid sequences and their functional variations are known.With respect to the heavy chain, in some embodiments, the heavy chain ofan antibody described herein can be an alpha (α), delta (Δ), epsilon(ε), gamma (γ) or mu (μ) heavy chain. In some embodiments, the heavychain of an antibody described herein can comprise a human alpha (α),delta (Δ), epsilon (ε), gamma (γ) or mu (μ) heavy chain. In a particularembodiment, an antibody described herein comprises a human gamma 1 CH1,CH2, and/or (e.g., and) CH3 domain. In some embodiments, the amino acidsequence of the VH domain comprises the amino acid sequence of a humangamma (γ) heavy chain constant region, such as any known in the art.Non-limiting examples of human constant region sequences have beendescribed in the art, e.g., see U.S. Pat. No. 5,693,780 and Kabat E A etal., (1991) supra. In some embodiments, the VH domain comprises an aminoacid sequence that is at least 70%, 75%, 80%, 85%, 90%, 95%, 98%, or atleast 99% identical to any of the variable chain constant regionsprovided herein. In some embodiments, an antibody is modified, e.g.,modified via glycosylation, phosphorylation, sumoylation, and/or (e.g.,and) methylation. In some embodiments, an antibody is a glycosylatedantibody, which is conjugated to one or more sugar or carbohydratemolecules. In some embodiments, the one or more sugar or carbohydratemolecule are conjugated to the antibody via N-glycosylation,O-glycosylation, C-glycosylation, glypiation (GPI anchor attachment),and/or (e.g., and) phosphoglycosylation. In some embodiments, the one ormore sugar or carbohydrate molecule are monosaccharides, disaccharides,oligosaccharides, or glycans. In some embodiments, the one or more sugaror carbohydrate molecule is a branched oligosaccharide or a branchedglycan. In some embodiments, the one or more sugar or carbohydratemolecule includes a mannose unit, a glucose unit, an N-acetylglucosamineunit, an N-acetylgalactosamine unit, a galactose unit, a fucose unit, ora phospholipid unit. In some embodiments, an antibody is a constructthat comprises a polypeptide comprising one or more antigen bindingfragments of the disclosure linked to a linker polypeptide or animmunoglobulin constant domain. Linker polypeptides comprise two or moreamino acid residues joined by peptide bonds and are used to link one ormore antigen binding portions. Examples of linker polypeptides have beenreported (see e.g., Holliger, P., et al. (1993) Proc. Natl. Acad. Sci.USA 90:6444-6448; Poljak, R. J., et al. (1994) Structure 2:1121-1123).Still further, an antibody may be part of a larger immunoadhesionmolecule, formed by covalent or noncovalent association of the antibodyor antibody portion with one or more other proteins or peptides.Examples of such immunoadhesion molecules include use of thestreptavidin core region to make a tetrameric scFv molecule (Kipriyanov,S. M., et al. (1995) Human Antibodies and Hybridomas 6:93-101) and useof a cysteine residue, a marker peptide and a C-terminal polyhistidinetag to make bivalent and biotinylated scFv molecules (Kipriyanov, S. M.,et al. (1994) Mol. Immunol. 31:1047-1058).

CDR: As used herein, the term “CDR” refers to the complementaritydetermining region within antibody variable sequences. A typicalantibody molecule comprises a heavy chain variable region (VH) and alight chain variable region (VL), which are usually involved in antigenbinding. The VH and VL regions can be further subdivided into regions ofhypervariability, also known as “complementarity determining regions”(“CDR”), interspersed with regions that are more conserved, which areknown as “framework regions” (“FR”). Each VH and VL is typicallycomposed of three CDRs and four FRs, arranged from amino-terminus tocarboxy-terminus in the following order: FR1, CDR1, FR2, CDR2, FR3,CDR3, FR4. The extent of the framework region and CDRs can be preciselyidentified using methodology known in the art, for example, by the Kabatdefinition, the IMGT definition, the Chothia definition, the AbMdefinition, and/or (e.g., and) the contact definition, all of which arewell known in the art. See, e.g., Kabat, E. A., et al. (1991) Sequencesof Proteins of Immunological Interest, Fifth Edition, U.S. Department ofHealth and Human Services, NIH Publication No. 91-3242; IMGT®, theinternational ImMunoGeneTics information System® http://www.imgt.org,Lefranc, M.-P. et al., Nucleic Acids Res., 27:209-212 (1999); Ruiz, M.et al., Nucleic Acids Res., 28:219-221 (2000); Lefranc, M.-P., NucleicAcids Res., 29:207-209 (2001); Lefranc, M.-P., Nucleic Acids Res.,31:307-310 (2003); Lefranc, M.-P. et al., In Silico Biol., 5, 0006(2004) [Epub], 5:45-60 (2005); Lefranc, M.-P. et al., Nucleic AcidsRes., 33:D593-597 (2005); Lefranc, M.-P. et al., Nucleic Acids Res.,37:D1006-1012 (2009); Lefranc, M.-P. et al., Nucleic Acids Res.,43:D413-422 (2015); Chothia et al., (1989) Nature 342:877; Chothia, C.et al. (1987) J. Mol. Biol. 196:901-917, Al-lazikani et al (1997) J.Molec. Biol. 273:927-948; and Almagro, J. Mol. Recognit. 17:132-143(2004). ee also hgmp.mrc.ac.uk and bioinf.org.uk/abs. As used herein, aCDR may refer to the CDR defined by any method known in the art. Twoantibodies having the same CDR means that the two antibodies have thesame amino acid sequence of that CDR as determined by the same method,for example, the IMGT definition.

There are three CDRs in each of the variable regions of the heavy chainand the light chain, which are designated CDR1, CDR2 and CDR3, for eachof the variable regions. The term “CDR set” as used herein refers to agroup of three CDRs that occur in a single variable region capable ofbinding the antigen. The exact boundaries of these CDRs have beendefined differently according to different systems. The system describedby Kabat (Kabat et al., Sequences of Proteins of Immunological Interest(National Institutes of Health, Bethesda, Md. (1987) and (1991)) notonly provides an unambiguous residue numbering system applicable to anyvariable region of an antibody, but also provides precise residueboundaries defining the three CDRs. These CDRs may be referred to asKabat CDRs. Sub-portions of CDRs may be designated as L1, L2 and L3 orH1, H2 and H3 where the “L” and the “H” designates the light chain andthe heavy chains regions, respectively. These regions may be referred toas Chothia CDRs, which have boundaries that overlap with Kabat CDRs.Other boundaries defining CDRs overlapping with the Kabat CDRs have beendescribed by Padlan (FASEB J. 9:133-139 (1995)) and MacCallum (J MolBiol 262(5):732-45 (1996)). Still other CDR boundary definitions may notstrictly follow one of the above systems, but will nonetheless overlapwith the Kabat CDRs, although they may be shortened or lengthened inlight of prediction or experimental findings that particular residues orgroups of residues or even entire CDRs do not significantly impactantigen binding. The methods used herein may utilize CDRs definedaccording to any of these systems. Examples of CDR definition systemsare provided in Table 1.

TABLE 1 CDR Definitions IMGT¹ Kabat² Chothia³ CDR-H1 27-38 31-35 26-32CDR-H2 56-65 50-65 53-55 CDR-H3    105-116/117  95-102  96-101 CDR-L127-38 24-34 26-32 CDR-L2 56-65 50-56 50-52 CDR-L3    105-116/117 89-9791-96 ¹IMGT ®, the international ImMunoGeneTics information system ®,imgt.org, Lefranc, M.-P. et al., Nucleic Acids Res., 27: 209-212 (1999)²Kabat et al. (1991) Sequences of Proteins of Immunological Interest,Fifth Edition, U.S. Department of Health and Human Services, NIHPublication No. 91-3242 ³Chothia et al., J. Mol. Biol. 196: 901-917(1987))

CDR-grafted antibody: The term “CDR-grafted antibody” refers toantibodies which comprise heavy and light chain variable regionsequences from one species but in which the sequences of one or more ofthe CDR regions of VH and/or (e.g., and) VL are replaced with CDRsequences of another species, such as antibodies having murine heavy andlight chain variable regions in which one or more of the murine CDRs(e.g., CDR3) has been replaced with human CDR sequences.

Chimeric antibody: The term “chimeric antibody” refers to antibodieswhich comprise heavy and light chain variable region sequences from onespecies and constant region sequences from another species, such asantibodies having murine heavy and light chain variable regions linkedto human constant regions.

Complementary: As used herein, the term “complementary” refers to thecapacity for precise pairing between two nucleotides or two sets ofnucleotides. In particular, complementary is a term that characterizesan extent of hydrogen bond pairing that brings about binding between twonucleotides or two sets of nucleotides. For example, if a base at oneposition of an oligonucleotide is capable of hydrogen bonding with abase at the corresponding position of a target nucleic acid (e.g., anmRNA), then the bases are considered to be complementary to each otherat that position. Base pairings may include both canonical Watson-Crickbase pairing and non-Watson-Crick base pairing (e.g., Wobble basepairing and Hoogsteen base pairing). For example, in some embodiments,for complementary base pairings, adenosine-type bases (A) arecomplementary to thymidine-type bases (T) or uracil-type bases (U), thatcytosine-type bases (C) are complementary to guanosine-type bases (G),and that universal bases such as 3-nitropyrrole or 5-nitroindole canhybridize to and are considered complementary to any A, C, U, or T.Inosine (I) has also been considered in the art to be a universal baseand is considered complementary to any A, C, U or T.

Conservative amino acid substitution: As used herein, a “conservativeamino acid substitution” refers to an amino acid substitution that doesnot alter the relative charge or size characteristics of the protein inwhich the amino acid substitution is made. Variants can be preparedaccording to methods for altering polypeptide sequence known to one ofordinary skill in the art such as are found in references which compilesuch methods, e.g. Molecular Cloning: A Laboratory Manual, J. Sambrook,et al., eds., Fourth Edition, Cold Spring Harbor Laboratory Press, ColdSpring Harbor, N.Y., 2012, or Current Protocols in Molecular Biology, F.M. Ausubel, et al., eds., John Wiley & Sons, Inc., New York.Conservative substitutions of amino acids include substitutions madeamongst amino acids within the following groups: (a) M, I, L, V; (b) F,Y, W; (c) K, R, H; (d) A, G; (e) S, T; (f) Q, N; and (g) E, D.

Covalently linked: As used herein, the term “covalently linked” refersto a characteristic of two or more molecules being linked together viaat least one covalent bond. In some embodiments, two molecules can becovalently linked together by a single bond, e.g., a disulfide bond ordisulfide bridge, that serves as a linker between the molecules.However, in some embodiments, two or more molecules can be covalentlylinked together via a molecule that serves as a linker that joins thetwo or more molecules together through multiple covalent bonds. In someembodiments, a linker may be a cleavable linker. However, in someembodiments, a linker may be a non-cleavable linker.

Cross-reactive: As used herein and in the context of a targeting agent(e.g., antibody), the term “cross-reactive,” refers to a property of theagent being capable of specifically binding to more than one antigen ofa similar type or class (e.g., antigens of multiple homologs, paralogs,or orthologs) with similar affinity or avidity. For example, in someembodiments, an antibody that is cross-reactive against human andnon-human primate antigens of a similar type or class (e.g., a humantransferrin receptor and non-human primate transferrin receptor) iscapable of binding to the human antigen and non-human primate antigenswith a similar affinity or avidity. In some embodiments, an antibody iscross-reactive against a human antigen and a rodent antigen of a similartype or class. In some embodiments, an antibody is cross-reactiveagainst a rodent antigen and a non-human primate antigen of a similartype or class. In some embodiments, an antibody is cross-reactiveagainst a human antigen, a non-human primate antigen, and a rodentantigen of a similar type or class.

DUX4: As used herein, the term “DUX4” refers to a gene that encodesdouble homeobox 4, a protein which is generally expressed during fetaldevelopment and in the testes of adult males. In some embodiments, DUX4may be a human (Gene ID: 100288687), non-human primate (e.g., Gene ID:750891, Gene ID: 100405864), or rodent gene (e.g., Gene ID: 306226). Inhumans, expression of the DUX4 gene outside of fetal development and thetestes is associated with facioscapulohumeral muscular dystrophy. Inaddition, multiple human transcript variants (e.g., as annotated underGenBank RefSeq Accession Numbers: NM_001293798.2, NM_001306068.2,NM_001363820.1) have been characterized that encode different proteinisoforms.

Facioscapulohumeral muscular dystrophy (FSHD): As used herein, the term“facioscapulohumeral muscular dystrophy (FSHD)” refers to a geneticdisease caused by mutations in the DUX4 gene or SMCHD1 gene that ischaracterized by muscle mass loss and muscle atrophy, primarily in themuscles of the face, shoulder blades, and upper arms. Two types of thedisease, Type 1 and Type 2, have been described. Type 1 is associatedwith deletions in D4Z4 repeat regions on chromosome 4 allelic variant4qA which contains the DUX4 gene. Type 2 is associated with mutations inthe SMCHD1 gene. Both Type 1 and Type 2 FSHD are characterized byaberrant production of the DUX4 protein after fetal development outsideof the testes. Facioscapulohumeral dystrophy, the genetic basis for thedisease, and related symptoms are described in the art (see, e.g.Campbell, A. E., et al., “Facioscapulohumeral dystrophy: Activating anearly embryonic transcriptional program in human skeletal muscle” HumanMol Genet. (2018); and Tawil, R. “Facioscapulohumeral musculardystrophy” Handbook Clin. Neurol. (2018), 148: 541-548.) FSHD Type 1 isassociated with Online Mendelian Inheritance in Man (OMIM) Entry#158900. FSHD Type 2 is associated with OMIM Entry #158901.

Framework: As used herein, the term “framework” or “framework sequence”refers to the remaining sequences of a variable region minus the CDRs.Because the exact definition of a CDR sequence can be determined bydifferent systems, the meaning of a framework sequence is subject tocorrespondingly different interpretations. The six CDRs (CDR-L1, CDR-L2,and CDR-L3 of light chain and CDR-H1, CDR-H2, and CDR-H3 of heavy chain)also divide the framework regions on the light chain and the heavy chaininto four sub-regions (FR1, FR2, FR3 and FR4) on each chain, in whichCDR1 is positioned between FR1 and FR2, CDR2 between FR2 and FR3, andCDR3 between FR3 and FR4. Without specifying the particular sub-regionsas FR1, FR2, FR3 or FR4, a framework region, as referred by others,represents the combined FRs within the variable region of a single,naturally occurring immunoglobulin chain. As used herein, a FRrepresents one of the four sub-regions, and FRs represents two or moreof the four sub-regions constituting a framework region. Human heavychain and light chain acceptor sequences are known in the art. In oneembodiment, the acceptor sequences known in the art may be used in theantibodies disclosed herein.

Human antibody: The term “human antibody”, as used herein, is intendedto include antibodies having variable and constant regions derived fromhuman germline immunoglobulin sequences. The human antibodies of thedisclosure may include amino acid residues not encoded by human germlineimmunoglobulin sequences (e.g., mutations introduced by random orsite-specific mutagenesis in vitro or by somatic mutation in vivo), forexample in the CDRs and in particular CDR3. However, the term “humanantibody”, as used herein, is not intended to include antibodies inwhich CDR sequences derived from the germline of another mammalianspecies, such as a mouse, have been grafted onto human frameworksequences.

Humanized antibody: The term “humanized antibody” refers to antibodieswhich comprise heavy and light chain variable region sequences from anon-human species (e.g., a mouse) but in which at least a portion of theVH and/or (e.g., and) VL sequence has been altered to be more“human-like”, i.e., more similar to human germline variable sequences.One type of humanized antibody is a CDR-grafted antibody, in which humanCDR sequences are introduced into non-human VH and VL sequences toreplace the corresponding nonhuman CDR sequences. In one embodiment,humanized anti-transferrin receptor antibodies and antigen bindingportions are provided. Such antibodies may be generated by obtainingmurine anti-transferrin receptor monoclonal antibodies using traditionalhybridoma technology followed by humanization using in vitro geneticengineering, such as those disclosed in Kasaian et al PCT publicationNo. WO 2005/123126 A2.

Internalizing cell surface receptor: As used herein, the term,“internalizing cell surface receptor” refers to a cell surface receptorthat is internalized by cells, e.g., upon external stimulation, e.g.,ligand binding to the receptor. In some embodiments, an internalizingcell surface receptor is internalized by endocytosis. In someembodiments, an internalizing cell surface receptor is internalized byclathrin-mediated endocytosis. However, in some embodiments, aninternalizing cell surface receptor is internalized by aclathrin-independent pathway, such as, for example, phagocytosis,macropinocytosis, caveolae- and raft-mediated uptake or constitutiveclathrin-independent endocytosis. In some embodiments, the internalizingcell surface receptor comprises an intracellular domain, a transmembranedomain, and/or (e.g., and) an extracellular domain, which may optionallyfurther comprise a ligand-binding domain. In some embodiments, a cellsurface receptor becomes internalized by a cell after ligand binding. Insome embodiments, a ligand may be a muscle-targeting agent or amuscle-targeting antibody. In some embodiments, an internalizing cellsurface receptor is a transferrin receptor.

Isolated antibody: An “isolated antibody”, as used herein, is intendedto refer to an antibody that is substantially free of other antibodieshaving different antigenic specificities (e.g., an isolated antibodythat specifically binds transferrin receptor is substantially free ofantibodies that specifically bind antigens other than transferrinreceptor). An isolated antibody that specifically binds transferrinreceptor complex may, however, have cross-reactivity to other antigens,such as transferrin receptor molecules from other species. Moreover, anisolated antibody may be substantially free of other cellular materialand/or (e.g., and) chemicals.

Kabat numbering: The terms “Kabat numbering”, “Kabat definitions and“Kabat labeling” are used interchangeably herein. These terms, which arerecognized in the art, refer to a system of numbering amino acidresidues which are more variable (i.e. hypervariable) than other aminoacid residues in the heavy and light chain variable regions of anantibody, or an antigen binding portion thereof (Kabat et al. (1971)Ann. NY Acad, Sci. 190:382-391 and, Kabat, E. A., et al. (1991)Sequences of Proteins of Immunological Interest, Fifth Edition, U.S.Department of Health and Human Services, NIH Publication No. 91-3242).For the heavy chain variable region, the hypervariable region rangesfrom amino acid positions 31 to 35 for CDR1, amino acid positions 50 to65 for CDR2, and amino acid positions 95 to 102 for CDR3. For the lightchain variable region, the hypervariable region ranges from amino acidpositions 24 to 34 for CDR1, amino acid positions 50 to 56 for CDR2, andamino acid positions 89 to 97 for CDR3.

Molecular payload: As used herein, the term “molecular payload” refersto a molecule or species that functions to modulate a biologicaloutcome. In some embodiments, a molecular payload is linked to, orotherwise associated with a muscle-targeting agent. In some embodiments,the molecular payload is a small molecule, a protein, a peptide, anucleic acid, or an oligonucleotide. In some embodiments, the molecularpayload functions to modulate the transcription of a DNA sequence, tomodulate the expression of a protein, or to modulate the activity of aprotein. In some embodiments, the molecular payload is anoligonucleotide that comprises a strand having a region ofcomplementarity to a target gene.

Muscle-targeting agent: As used herein, the term, “muscle-targetingagent,” refers to a molecule that specifically binds to an antigenexpressed on muscle cells. The antigen in or on muscle cells may be amembrane protein, for example an integral membrane protein or aperipheral membrane protein. Typically, a muscle-targeting agentspecifically binds to an antigen on muscle cells that facilitatesinternalization of the muscle-targeting agent (and any associatedmolecular payload) into the muscle cells. In some embodiments, amuscle-targeting agent specifically binds to an internalizing, cellsurface receptor on muscles and is capable of being internalized intomuscle cells through receptor mediated internalization. In someembodiments, the muscle-targeting agent is a small molecule, a protein,a peptide, a nucleic acid (e.g., an aptamer), or an antibody. In someembodiments, the muscle-targeting agent is linked to a molecularpayload.

Muscle-targeting antibody: As used herein, the term, “muscle-targetingantibody,” refers to a muscle-targeting agent that is an antibody thatspecifically binds to an antigen found in or on muscle cells. In someembodiments, a muscle-targeting antibody specifically binds to anantigen on muscle cells that facilitates internalization of themuscle-targeting antibody (and any associated molecular payment) intothe muscle cells. In some embodiments, the muscle-targeting antibodyspecifically binds to an internalizing, cell surface receptor present onmuscle cells. In some embodiments, the muscle-targeting antibody is anantibody that specifically binds to a transferrin receptor.

Oligonucleotide: As used herein, the term “oligonucleotide” refers to anoligomeric nucleic acid compound of up to 200 nucleotides in length.Examples of oligonucleotides include, but are not limited to, RNAioligonucleotides (e.g., siRNAs, shRNAs), microRNAs, gapmers, mixmers,phosphorodiamidate morpholinos, peptide nucleic acids, aptamers, guidenucleic acids (e.g., Cas9 guide RNAs), etc. Oligonucleotides may besingle-stranded or double-stranded. In some embodiments, anoligonucleotide may comprise one or more modified nucleotides ornucleosides (e.g. 2′-O-methyl sugar modifications, purine or pyrimidinemodifications). In some embodiments, an oligonucleotide may comprise oneor more modified internucleotide linkages. In some embodiments, anoligonucleotide may comprise one or more phosphorothioate linkages,which may be in the Rp or Sp stereochemical conformation.

Recombinant antibody: The term “recombinant human antibody”, as usedherein, is intended to include all human antibodies that are prepared,expressed, created or isolated by recombinant means, such as antibodiesexpressed using a recombinant expression vector transfected into a hostcell (described in more details in this disclosure), antibodies isolatedfrom a recombinant, combinatorial human antibody library (Hoogenboom H.R., (1997) TIB Tech. 15:62-70; Azzazy H., and Highsmith W. E., (2002)Clin. Biochem. 35:425-445; Gavilondo J. V., and Larrick J. W. (2002)BioTechniques 29:128-145; Hoogenboom H., and Chames P. (2000) ImmunologyToday 21:371-378), antibodies isolated from an animal (e.g., a mouse)that is transgenic for human immunoglobulin genes (see e.g., Taylor, L.D., et al. (1992) Nucl. Acids Res. 20:6287-6295; Kellermann S-A., andGreen L. L. (2002) Current Opinion in Biotechnology 13:593-597; LittleM. et al (2000) Immunology Today 21:364-370) or antibodies prepared,expressed, created or isolated by any other means that involves splicingof human immunoglobulin gene sequences to other DNA sequences. Suchrecombinant human antibodies have variable and constant regions derivedfrom human germline immunoglobulin sequences. In certain embodiments,however, such recombinant human antibodies are subjected to in vitromutagenesis (or, when an animal transgenic for human Ig sequences isused, in vivo somatic mutagenesis) and thus the amino acid sequences ofthe VH and VL regions of the recombinant antibodies are sequences that,while derived from and related to human germline VH and VL sequences,may not naturally exist within the human antibody germline repertoire invivo. One embodiment of the disclosure provides fully human antibodiescapable of binding human transferrin receptor which can be generatedusing techniques well known in the art, such as, but not limited to,using human Ig phage libraries such as those disclosed in Jermutus etal., PCT publication No. WO 2005/007699 A2.

Region of complementarity: As used herein, the term “region ofcomplementarity” refers to a nucleotide sequence, e.g., of aoligonucleotide, that is sufficiently complementary to a cognatenucleotide sequence, e.g., of a target nucleic acid, such that the twonucleotide sequences are capable of annealing to one another underphysiological conditions (e.g., in a cell). In some embodiments, aregion of complementarity is fully complementary to a cognate nucleotidesequence of target nucleic acid. However, in some embodiments, a regionof complementarity is partially complementary to a cognate nucleotidesequence of target nucleic acid (e.g., at least 80%, 90%, 95% or 99%complementarity). In some embodiments, a region of complementaritycontains 1, 2, 3, or 4 mismatches compared with a cognate nucleotidesequence of a target nucleic acid.

Specifically binds: As used herein, the term “specifically binds” refersto the ability of a molecule to bind to a binding partner with a degreeof affinity or avidity that enables the molecule to be used todistinguish the binding partner from an appropriate control in a bindingassay or other binding context. With respect to an antibody, the term,“specifically binds”, refers to the ability of the antibody to bind to aspecific antigen with a degree of affinity or avidity, compared with anappropriate reference antigen or antigens, that enables the antibody tobe used to distinguish the specific antigen from others, e.g., to anextent that permits preferential targeting to certain cells, e.g.,muscle cells, through binding to the antigen, as described herein. Insome embodiments, an antibody specifically binds to a target if theantibody has a K_(D) for binding the target of at least about 10⁻⁴ M,10⁻⁵ M, 10⁻⁶ M, 10⁻⁷ M, 10⁻⁸ M, 10⁻⁹ M, 10⁻¹⁰ M, 10⁻¹¹ M, 10⁻¹² M, 10⁻¹³M, or less. In some embodiments, an antibody specifically binds to thetransferrin receptor, e.g., an epitope of the apical domain oftransferrin receptor.

Subject: As used herein, the term “subject” refers to a mammal. In someembodiments, a subject is non-human primate, or rodent. In someembodiments, a subject is a human. In some embodiments, a subject is apatient, e.g., a human patient that has or is suspected of having adisease. In some embodiments, the subject is a human patient who has oris suspected of having FSHD.

Transferrin receptor: As used herein, the term, “transferrin receptor”(also known as TFRC, CD71, p90, TFR or TFR1) refers to an internalizingcell surface receptor that binds transferrin to facilitate iron uptakeby endocytosis. In some embodiments, a transferrin receptor may be ofhuman (NCBI Gene ID 7037), non-human primate (e.g., NCBI Gene ID 711568or NCBI Gene ID 102136007), or rodent (e.g., NCBI Gene ID 22042) origin.In addition, multiple human transcript variants have been characterizedthat encoded different isoforms of the receptor (e.g., as annotatedunder GenBank RefSeq Accession Numbers: NP_001121620.1, NP_003225.2,NP_001300894.1, and NP_001300895.1).

2′-modified nucleoside: As used herein, the terms “2′-modifiednucleoside” and “2′-modified ribonucleoside” are used interchangeablyand refer to a nucleoside having a sugar moiety modified at the 2′position. In some embodiments, the 2′-modified nucleoside is a 2′-4′bicyclic nucleoside, where the 2′ and 4′ positions of the sugar arebridged (e.g., via a methylene, an ethylene, or a (S)-constrained ethylbridge). In some embodiments, the 2′-modified nucleoside is anon-bicyclic 2′-modified nucleoside, e.g., where the 2′ position of thesugar moiety is substituted. Non-limiting examples of 2′-modifiednucleosides include: 2′-deoxy, 2′-fluoro (2′-F), 2′-O-methyl (2′-O-Me),2′-O-methoxyethyl (2′-MOE), 2′-O-aminopropyl (2′-O-AP),2′-O-dimethylaminoethyl (2′-O-DMAOE), 2′-O-dimethylaminopropyl(2′-O-DMAP), 2′-O-dimethylaminoethyloxyethyl (2′-O-DMAEOE),2′-O—N-methylacetamido (2′-O-NMA), locked nucleic acid (LNA,methylene-bridged nucleic acid), ethylene-bridged nucleic acid (ENA),and (S)-constrained ethyl-bridged nucleic acid (cEt). In someembodiments, the 2′-modified nucleosides described herein arehigh-affinity modified nucleotides and oligonucleotides comprising the2′-modified nucleotides have increased affinity to a target sequences,relative to an unmodified oligonucleotide. Examples of structures of2′-modified nucleosides are provided below:

II. Complexes

Provided herein are complexes that comprise a targeting agent, e.g. anantibody, covalently linked to a molecular payload. In some embodiments,a complex comprises a muscle-targeting antibody covalently linked to anoligonucleotide. A complex may comprise an antibody that specificallybinds a single antigenic site or that binds to at least two antigenicsites that may exist on the same or different antigens.

A complex may be used to modulate the activity or function of at leastone gene, protein, and/or (e.g., and) nucleic acid. In some embodiments,the molecular payload present with a complex is responsible for themodulation of a gene, protein, and/or (e.g., and) nucleic acids. Amolecular payload may be a small molecule, protein, nucleic acid,oligonucleotide, or any molecular entity capable of modulating theactivity or function of a gene, protein, and/or (e.g., and) nucleic acidin a cell. In some embodiments, a molecular payload is anoligonucleotide that targets a DUX4 in muscle cells.

In some embodiments, a complex comprises a muscle-targeting agent, e.g.an anti-transferrin receptor antibody, covalently linked to a molecularpayload, e.g. an antisense oligonucleotide that targets a DUX4.

A. Muscle-Targeting Agents

Some aspects of the disclosure provide muscle-targeting agents, e.g.,for delivering a molecular payload to a muscle cell. In someembodiments, such muscle-targeting agents are capable of binding to amuscle cell, e.g., via specifically binding to an antigen on the musclecell, and delivering an associated molecular payload to the muscle cell.In some embodiments, the molecular payload is bound (e.g., covalentlybound) to the muscle targeting agent and is internalized into the musclecell upon binding of the muscle targeting agent to an antigen on themuscle cell, e.g., via endocytosis. It should be appreciated thatvarious types of muscle-targeting agents may be used in accordance withthe disclosure. For example, the muscle-targeting agent may comprise, orconsist of, a nucleic acid (e.g., DNA or RNA), a peptide (e.g., anantibody), a lipid (e.g., a microvesicle), or a sugar moiety (e.g., apolysaccharide). Exemplary muscle-targeting agents are described infurther detail herein, however, it should be appreciated that theexemplary muscle-targeting agents provided herein are not meant to belimiting.

Some aspects of the disclosure provide muscle-targeting agents thatspecifically bind to an antigen on muscle, such as skeletal muscle,smooth muscle, or cardiac muscle. In some embodiments, any of themuscle-targeting agents provided herein bind to (e.g., specifically bindto) an antigen on a skeletal muscle cell, a smooth muscle cell, and/or(e.g., and) a cardiac muscle cell.

By interacting with muscle-specific cell surface recognition elements(e.g., cell membrane proteins), both tissue localization and selectiveuptake into muscle cells can be achieved. In some embodiments, moleculesthat are substrates for muscle uptake transporters are useful fordelivering a molecular payload into muscle tissue. Binding to musclesurface recognition elements followed by endocytosis can allow evenlarge molecules such as antibodies to enter muscle cells. As anotherexample molecular payloads conjugated to transferrin or anti-transferrinreceptor antibodies can be taken up by muscle cells via binding totransferrin receptor, which may then be endocytosed, e.g., viaclathrin-mediated endocytosis.

The use of muscle-targeting agents may be useful for concentrating amolecular payload (e.g., oligonucleotide) in muscle while reducingtoxicity associated with effects in other tissues. In some embodiments,the muscle-targeting agent concentrates a bound molecular payload inmuscle cells as compared to another cell type within a subject. In someembodiments, the muscle-targeting agent concentrates a bound molecularpayload in muscle cells (e.g., skeletal, smooth, or cardiac musclecells) in an amount that is at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15,20, 30, 40, 50, 60, 70, 80, 90, or 100 times greater than an amount innon-muscle cells (e.g., liver, neuronal, blood, or fat cells). In someembodiments, a toxicity of the molecular payload in a subject is reducedby at least 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%,50%, 55%, 60%, 65%, 70%, 75%, 80%, 90%, or 95% when it is delivered tothe subject when bound to the muscle-targeting agent.

In some embodiments, to achieve muscle selectivity, a muscle recognitionelement (e.g., a muscle cell antigen) may be required. As one example, amuscle-targeting agent may be a small molecule that is a substrate for amuscle-specific uptake transporter. As another example, amuscle-targeting agent may be an antibody that enters a muscle cell viatransporter-mediated endocytosis. As another example, a muscle targetingagent may be a ligand that binds to cell surface receptor on a musclecell. It should be appreciated that while transporter-based approachesprovide a direct path for cellular entry, receptor-based targeting mayinvolve stimulated endocytosis to reach the desired site of action.

i. Muscle-Targeting Antibodies

In some embodiments, the muscle-targeting agent is an antibody.Generally, the high specificity of antibodies for their target antigenprovides the potential for selectively targeting muscle cells (e.g.,skeletal, smooth, and/or (e.g., and) cardiac muscle cells). Thisspecificity may also limit off-target toxicity. Examples of antibodiesthat are capable of targeting a surface antigen of muscle cells havebeen reported and are within the scope of the disclosure. For example,antibodies that target the surface of muscle cells are described inArahata K., et al. “Immunostaining of skeletal and cardiac musclesurface membrane with antibody against Duchenne muscular dystrophypeptide” Nature 1988; 333: 861-3; Song K. S., et al. “Expression ofcaveolin-3 in skeletal, cardiac, and smooth muscle cells. Caveolin-3 isa component of the sarcolemma and co-fractionates with dystrophin anddystrophin-associated glycoproteins” J Biol Chem 1996; 271: 15160-5; andWeisbart R. H. et al., “Cell type specific targeted intracellulardelivery into muscle of a monoclonal antibody that binds myosin IIb” MolImmunol. 2003 March, 39(13):78309; the entire contents of each of whichare incorporated herein by reference.

a. Anti-Transferrin Receptor Antibodies

Some aspects of the disclosure are based on the recognition that agentsbinding to transferrin receptor, e.g., anti-transferrin-receptorantibodies, are capable of targeting muscle cell. Transferrin receptorsare internalizing cell surface receptors that transport transferrinacross the cellular membrane and participate in the regulation andhomeostasis of intracellular iron levels. Some aspects of the disclosureprovide transferrin receptor binding proteins, which are capable ofbinding to transferrin receptor. Accordingly, aspects of the disclosureprovide binding proteins (e.g., antibodies) that bind to transferrinreceptor. In some embodiments, binding proteins that bind to transferrinreceptor are internalized, along with any bound molecular payload, intoa muscle cell. As used herein, an antibody that binds to a transferrinreceptor may be referred to interchangeably as an, transferrin receptorantibody, an anti-transferrin receptor antibody, or an anti-TfRantibody. Antibodies that bind, e.g. specifically bind, to a transferrinreceptor may be internalized into the cell, e.g. throughreceptor-mediated endocytosis, upon binding to a transferrin receptor.

It should be appreciated that anti-transferrin receptor antibodies maybe produced, synthesized, and/or (e.g., and) derivatized using severalknown methodologies, e.g. library design using phage display. Exemplarymethodologies have been characterized in the art and are incorporated byreference (Diez, P. et al. “High-throughput phage-display screening inarray format”, Enzyme and microbial technology, 2015, 79, 34-41; Hammerset al., “Antibody Phage Display: Technique and Applications” J InvestDermatol. 2014, 134:2; Engleman, Edgar (Ed.) “Human Hybridomas andMonoclonal Antibodies.” 1985, Springer.). In other embodiments, ananti-transferrin antibody has been previously characterized ordisclosed. Antibodies that specifically bind to transferrin receptor areknown in the art (see, e.g. U.S. Pat. No. 4,364,934, filed Dec. 4, 1979,“Monoclonal antibody to a human early thymocyte antigen and methods forpreparing same”; U.S. Pat. No. 8,409,573, filed Jun. 14, 2006,“Anti-CD71 monoclonal antibodies and uses thereof for treating malignanttumor cells”; U.S. Pat. No. 9,708,406, filed May 20, 2014,“Anti-transferrin receptor antibodies and methods of use”; U.S. Pat. No.9,611,323, filed Dec. 19, 2014, “Low affinity blood brain barrierreceptor antibodies and uses therefor”; WO 2015/098989, filed Dec. 24,2014, “Novel anti-Transferrin receptor antibody that passes throughblood-brain barrier”; Schneider C. et al. “Structural features of thecell surface receptor for transferrin that is recognized by themonoclonal antibody OKT9.” J Biol Chem. 1982, 257:14, 8516-8522.; Lee etal. “Targeting Rat Anti-Mouse Transferrin Receptor Monoclonal Antibodiesthrough Blood-Brain Barrier in Mouse” 2000, J Pharmacol. Exp. Ther.,292: 1048-1052.).

Provided herein, in some aspects, are new anti-TfR antibodies for use asthe muscle targeting agents (e.g., in muscle targeting complexes). Insome embodiments, the anti-TfR antibody described herein binds totransferrin receptor with high specificity and affinity. In someembodiments, the anti-TfR antibody described herein specifically bindsto any extracellular epitope of a transferrin receptor or an epitopethat becomes exposed to an antibody. In some embodiments, anti-TfRantibodies provided herein bind specifically to transferrin receptorfrom human, non-human primates, mouse, rat, etc. In some embodiments,anti-TfR antibodies provided herein bind to human transferrin receptor.In some embodiments, the anti-TfR antibody described herein binds to anamino acid segment of a human or non-human primate transferrin receptor,as provided in SEQ ID NOs: 105-108. In some embodiments, the anti-TfRantibody described herein binds to an amino acid segment correspondingto amino acids 90-96 of a human transferrin receptor as set forth in SEQID NO: 105, which is not in the apical domain of the transferrinreceptor.

corresponding to NCBI sequence NP_003225.2 (transferrin receptor protein1 isoform 1, Homo sapiens) is as follows:

(SEQ ID NO: 105)MMDQARSAFSNLFGGEPLSYTRFSLARQVDGDNSHVEMKLAVDEEENADNNTKANVTKPKRCSGSICYGTIAVIVFFLIGFMIGYLGYCKGVEPKTECERLAGTESPVREEPGEDFPAARRLYWDDLKRKLSEKLDSTDFTGTIKLLNENSYVPREAGSQKDENLALYVENQFREFKLSKVWRDQHFVKIQVKDSAQNSVIIVDKNGRLVYLVENPGGYVAYSKAATVTGKLVHANFGTKKDFEDLYTPVNGSIVIVRAGKITFAEKVANAESLNAIGVLIYMDQTKFPIVNAELSFFGHAHLGTGDPYTPGFPSFNHTQFPPSRSSGLPNIPVQTISRAAAEKLFGNMEGDCPSDWKTDSTCRMVTSESKNVKLTVSNVLKEIKILNIFGVIKGFVEPDHYVVVGAQRDAWGPGAAKSGVGTALLLKLAQMFSDMVLKDGFQPSRSIIFASWSAGDFGSVGATEWLEGYLSSLHLKAFTYINLDKAVLGTSNFKVSASPLLYTLIEKTMQNVKHPVTGQFLYQDSNWASKVEKLTLDNAAFPFLAYSGIPAVSFCFCEDTDYPYLGTTMDTYKELIERIPELNKVARAAAEVAGQFVIKLTHDVELNLDYERYNSQLLSFVRDLNQYRADIKEMGLSLQWLYSARGDFFRATSRLTTDFGNAEKTDRFVMKKLNDRVMRVEYHFLSPYVSPKESPFRHVFWGSGSHTLPALLENLKLRKQNNGAFNETLFRNQLALATWTIQGAANALSGDVWDIDNEF.

An example non-human primate transferrin receptor amino acid sequence,corresponding to NCBI sequence NP_001244232.1 (transferrin receptorprotein 1, Macaca mulatta) is as follows:

(SEQ ID NO: 106)MMDQARSAFSNLFGGEPLSYTRFSLARQVDGDNSHVEMKLGVDEEENTDNNTKPNGTKPKRCGGNICYGTIAVIIFFLIGFMIGYLGYCKGVEPKTECERLAGTESPAREEPEEDFPAAPRLYWDDLKRKLSEKLDTTDFTSTIKLLNENLYVPREAGSQKDENLALYIENQFREFKLSKVWRDQHFVKIQVKDSAQNSVIIVDKNGGLVYLVENPGGYVAYSKAATVTGKLVHANFGTKKDFEDLDSPVNGSIVIVRAGKITFAEKVANAESLNAIGVLIYMDQTKFPIVKADLSFFGHAHLGTGDPYTPGFPSFNHTQFPPSQSSGLPNIPVQTISRAAAEKLFGNMEGDCPSDWKTDSTCKMVTSENKSVKLTVSNVLKETKILNIFGVIKGFVEPDHYVVVGAQRDAWGPGAAKSSVGTALLLKLAQMFSDMVLKDGFQPSRSIIFASWSAGDFGSVGATEWLEGYLSSLHLKAFTYINLDKAVLGTSNFKVSASPLLYTLIEKTMQDVKHPVTGRSLYQDSNWASKVEKLTLDNAAFPFLAYSGIPAVSFCFCEDTDYPYLGTTMDTYKELVERIPELNKVARAAAEVAGQFVIKLTHDTELNLDYERYNSQLLLFLRDLNQYRADVKEMGLSLQWLYSARGDFFRATSRLTTDFRNAEKRDKFVMKKLNDRVMRVEYYFLSPYVSPKESPFRHVFWGSGSHTLSALLESLKLRRQNNSAFNETLFRNQLALATWTIQGAANALSGDVWDIDNEF

An example non-human primate transferrin receptor amino acid sequence,corresponding to NCBI sequence XP_005545315.1 (transferrin receptorprotein 1, Macaca fascicularis) is as follows:

(SEQ ID NO: 107)MMDQARSAFSNLFGGEPLSYTRFSLARQVDGDNSHVEMKLGVDEEENTDNNTKANGTKPKRCGGNICYGTIAVIIFFLIGFMIGYLGYCKGVEPKTECERLAGTESPAREEPEEDFPAAPRLYWDDLKRKLSEKLDTTDFTSTIKLLNENLYVPREAGSQKDENLALYIENQFREFKLSKVWRDQHFVKIQVKDSAQNSVIIVDKNGGLVYLVENPGGYVAYSKAATVTGKLVHANFGTKKDFEDLDSPVNGSIVIVRAGKITFAEKVANAESLNAIGVLIYMDQTKFPIVKADLSFFGHAHLGTGDPYTPGFPSFNHTQFPPSQSSGLPNIPVQTISRAAAEKLFGNMEGDCPSDWKTDSTCKMVTSENKSVKLTVSNVLKETKILNIFGVIKGFVEPDHYVVVGAQRDAWGPGAAKSSVGTALLLKLAQMFSDMVLKDGFQPSRSIIFASWSAGDFGSVGATEWLEGYLSSLHLKAFTYINLDKAVLGTSNFKVSASPLLYTLIEKTMQDVKHPVTGRSLYQDSNWASKVEKLTLDNAAFPFLAYSGIPAVSFCFCEDTDYPYLGTTMDTYKELVERIPELNKVARAAAEVAGQFVIKLTHDTELNLDYERYNSQLLLFLRDLNQYRADVKEMGLSLQWLYSARGDFFRATSRLTTDFRNAEKRDKFVMKKLNDRVMRVEYYFLSPYVSPKESPFRHVFWGSGSHTLSALLESLKLRRQNNSAFNETLFRNQLALATWTIQGAANALSGDVWDIDNEF.

An example mouse transferrin receptor amino acid sequence, correspondingto NCBI sequence NP_001344227.1 (transferrin receptor protein 1, Musmusculus) is as follows:

(SEQ ID NO: 108)MMDQARSAFSNLFGGEPLSYTRFSLARQVDGDNSHVEMKLAADEEENADNNMKASVRKPKRFNGRLCFAAIALVIFFLIGFMSGYLGYCKRVEQKEECVKLAETEETDKSETMETEDVPTSSRLYWADLKTLLSEKLNSIEFADTIKQLSQNTYTPREAGSQKDESLAYYIENQFHEFKFSKVWRDEHYVKIQVKSSIGQNMVTIVQSNGNLDPVESPEGYVAFSKPTEVSGKLVHANFGTKKDFEELSYSVNGSLVIVRAGEITFAEKVANAQSFNAIGVLIYMDKNKFPVVEADLALFGHAHLGTGDPYTPGFPSFNHTQFPPSQSSGLPNIPVQTISRAAAEKLFGKMEGSCPARWNIDSSCKLELSQNQNVKLIVKNVLKERRILNIFGVIKGYEEPDRYVVVGAQRDALGAGVAAKSSVGTGLLLKLAQVFSDMISKDGFRPSRSIIFASWTAGDFGAVGATEWLEGYLSSLHLKAFTYINLDKVVLGTSNFKVSASPLLYTLMGKIMQDVKHPVDGKSLYRDSNWISKVEKLSFDNAAYPFLAYSGIPAVSFCFCEDADYPYLGTRLDTYEALTQKVPQLNQMVRTAAEVAGQLIIKLTHDVELNLDYEMYNSKLLSFMKDLNQFKTDIRDMGLSLQWLYSARGDYFRATSRLTTDFHNAEKTNRFVMREINDRIMKVEYHFLSPYVSPRESPFRHIFWGSGSHTLSALVENLKLRQKNITAFNETLFRNQLALATWTIQGVANALSGDIWNIDNEF

In some embodiments, an anti-transferrin receptor antibody binds to anamino acid segment of the receptor as follows:

FVKIQVKDSAQNSVIIVDKNGRLVYLVENPGGYVAYSKAATVTGKLVHANFGTKKDFEDLYTPVNGSIVIVRAGKITFAEKVANAESLNAIGVLIYMDQTKFPIVNAELSFFGHAHLGTGDPYTPGFPSFNHTQFPPSRSSGLPNIPVQTISRAAAEKLFGNMEGDCPSDWKTDSTCRMVTSESKNVKLTVSNVLKE (SEQ ID NO: 109) and does not inhibit the bindinginteractions between transferrin receptors and transferrin and/or (e.g.,and) human hemochromatosis protein (also known as HFE). In someembodiments, the anti-transferrin receptor antibody described hereindoes not bind an epitope in SEQ ID NO: 109.

Appropriate methodologies may be used to obtain and/or (e.g., and)produce antibodies, antibody fragments, or antigen-binding agents, e.g.,through the use of recombinant DNA protocols. In some embodiments, anantibody may also be produced through the generation of hybridomas (see,e.g., Kohler, G and Milstein, C. “Continuous cultures of fused cellssecreting antibody of predefined specificity” Nature, 1975, 256:495-497). The antigen-of-interest may be used as the immunogen in anyform or entity, e.g., recombinant or a naturally occurring form orentity. Hybridomas are screened using standard methods, e.g. ELISAscreening, to find at least one hybridoma that produces an antibody thattargets a particular antigen. Antibodies may also be produced throughscreening of protein expression libraries that express antibodies, e.g.,phage display libraries. Phage display library design may also be used,in some embodiments, (see, e.g. U.S. Pat. No. 5,223,409, filed Mar. 1,1991, “Directed evolution of novel binding proteins”; WO 1992/18619,filed Apr. 10, 1992, “Heterodimeric receptor libraries using phagemids”;WO 1991/17271, filed May 1, 1991, “Recombinant library screeningmethods”; WO 1992/20791, filed May 15, 1992, “Methods for producingmembers of specific binding pairs”; WO 1992/15679, filed Feb. 28, 1992,and “Improved epitope displaying phage”). In some embodiments, anantigen-of-interest may be used to immunize a non-human animal, e.g., arodent or a goat. In some embodiments, an antibody is then obtained fromthe non-human animal, and may be optionally modified using a number ofmethodologies, e.g., using recombinant DNA techniques. Additionalexamples of antibody production and methodologies are known in the art(see, e.g. Harlow et al. “Antibodies: A Laboratory Manual”, Cold SpringHarbor Laboratory, 1988.).

In some embodiments, an antibody is modified, e.g., modified viaglycosylation, phosphorylation, sumoylation, and/or (e.g., and)methylation. In some embodiments, an antibody is a glycosylatedantibody, which is conjugated to one or more sugar or carbohydratemolecules. In some embodiments, the one or more sugar or carbohydratemolecule are conjugated to the antibody via N-glycosylation,O-glycosylation, C-glycosylation, glypiation (GPI anchor attachment),and/or (e.g., and) phosphoglycosylation. In some embodiments, the one ormore sugar or carbohydrate molecules are monosaccharides, disaccharides,oligosaccharides, or glycans. In some embodiments, the one or more sugaror carbohydrate molecule is a branched oligosaccharide or a branchedglycan. In some embodiments, the one or more sugar or carbohydratemolecule includes a mannose unit, a glucose unit, an N-acetylglucosamineunit, an N-acetylgalactosamine unit, a galactose unit, a fucose unit, ora phospholipid unit. In some embodiments, there are about 1-10, about1-5, about 5-10, about 1-4, about 1-3, or about 2 sugar molecules. Insome embodiments, a glycosylated antibody is fully or partiallyglycosylated. In some embodiments, an antibody is glycosylated bychemical reactions or by enzymatic means. In some embodiments, anantibody is glycosylated in vitro or inside a cell, which may optionallybe deficient in an enzyme in the N- or O-glycosylation pathway, e.g. aglycosyltransferase. In some embodiments, an antibody is functionalizedwith sugar or carbohydrate molecules as described in InternationalPatent Application Publication WO2014065661, published on May 1, 2014,entitled, “Modified antibody, antibody-conjugate and process for thepreparation thereof”.

In some embodiments, the anti-TfR antibody of the present disclosurecomprises a VL domain and/or (e.g., and) VH domain of any one of theanti-TfR antibodies selected from Table 2, and comprises a constantregion comprising the amino acid sequences of the constant regions of anIgG, IgE, IgM, IgD, IgA or IgY immunoglobulin molecule, any class (e.g.,IgG1, IgG2, IgG3, IgG4, IgA1 and IgA2), or any subclass (e.g., IgG2a andIgG2b) of immunoglobulin molecule. Non-limiting examples of humanconstant regions are described in the art, e.g., see Kabat E A et al.,(1991) supra.

In some embodiments, agents binding to transferrin receptor, e.g.,anti-TfR antibodies, are capable of targeting muscle cell and/or (e.g.,and) mediate the transportation of an agent across the blood brainbarrier. Transferrin receptors are internalizing cell surface receptorsthat transport transferrin across the cellular membrane and participatein the regulation and homeostasis of intracellular iron levels. Someaspects of the disclosure provide transferrin receptor binding proteins,which are capable of binding to transferrin receptor. Antibodies thatbind, e.g. specifically bind, to a transferrin receptor may beinternalized into the cell, e.g. through receptor-mediated endocytosis,upon binding to a transferrin receptor.

Provided herein, in some aspects, are humanized antibodies that bind totransferrin receptor with high specificity and affinity. In someembodiments, the humanized anti-TfR antibody described hereinspecifically binds to any extracellular epitope of a transferrinreceptor or an epitope that becomes exposed to an antibody. In someembodiments, the humanized anti-TfR antibodies provided herein bindspecifically to transferrin receptor from human, non-human primates,mouse, rat, etc. In some embodiments, the humanized anti-TfR antibodiesprovided herein bind to human transferrin receptor. In some embodiments,the humanized anti-TfR antibody described herein binds to an amino acidsegment of a human or non-human primate transferrin receptor, asprovided in SEQ ID NOs: 105-108. In some embodiments, the humanizedanti-TfR antibody described herein binds to an amino acid segmentcorresponding to amino acids 90-96 of a human transferrin receptor asset forth in SEQ ID NO: 105, which is not in the apical domain of thetransferrin receptor. In some embodiments, the humanized anti-TfRantibodies described herein binds to TfR1 but does not bind to TfR2.

In some embodiments, an anti-TFR antibody specifically binds a TfR1(e.g., a human or non-human primate TfR1) with binding affinity (e.g.,as indicated by Kd) of at least about 10⁴ M, 10⁻⁵ M, 10⁻⁶ M, 10⁻⁷ M,10⁻⁸ M, 10⁻⁹ M, 10⁻¹⁰ M, 10⁻¹¹ M, 10⁻¹² M, 10⁻¹³ M, or less. In someembodiments, the anti-TfR antibodies described herein binds to TfR1 witha KD of sub-nanomolar range. In some embodiments, the anti-TfRantibodies described herein selectively binds to transferrin receptor 1(TfR1) but do not bind to transferrin receptor 2 (TfR2). In someembodiments, the anti-TfR antibodies described herein binds to humanTfR1 and cyno TfR1 (e.g., with a Kd of 10⁻⁷ M, 10⁻⁸ M, 10⁻⁹ M, 10⁻¹⁰ M,10⁻¹¹ M, 10⁻¹² M, 10⁻¹³ M, or less), but does not bind to a mouse TfR1.The affinity and binding kinetics of the anti-TfR antibody can be testedusing any suitable method including but not limited to biosensortechnology (e.g., OCTET or BIACORE). In some embodiments, binding of anyone of the anti-TfR antibody described herein does not complete with orinhibit transferrin binding to the TfR1. In some embodiments, binding ofany one of the anti-TfR antibody described herein does not complete withor inhibit HFE-beta-2-microglobulin binding to the TfR1.

The anti-TfR antibodies described herein are humanized antibodies. TheCDR and variable region amino acid sequences of the mouse monoclonalanti-TfR antibody from which the humanized anti-TfR antibodies describedherein are derived are provided in Table 2.

TABLE 2 Mouse Monoclonal Anti-TfR Antibodies No. System Ab IMGT KabatChothia 3-A4 CDR- GFNIKDDY (SEQ ID NO: DDYMY (SEQ ID NO: 7)GFNIKDD (SEQ ID H1 1) NO: 12) CDR- IDPENGDT (SEQ ID NO:WIDPENGDTEYASKFQD ENG (SEQ ID NO: H2 2) (SEQ ID NO: 8) 13) CDR-TLWLRRGLDY (SEQ ID WLRRGLDY (SEQ ID NO: 9) LRRGLD (SEQ ID H3 NO: 3)NO: 14) CDR- KSLLHSNGYTY (SEQ ID RSSKSLLHSNGYTYLF (SEQ SKSLLHSNGYTY L1NO: 4) ID NO: 10) (SEQ ID NO: 15) CDR- RMS (SEQ ID NO: 5)RMSNLAS (SEQ ID NO: 11) RMS (SEQ ID NO: L2 5) CDR- MQHLEYPFT (SEQ IDMQHLEYPFT (SEQ ID NO: 6) HLEYPF (SEQ ID L3 NO: 6) NO: 16) VHEVQLQQSGAELVRPGASVKLSCTASGFNIKDDYMYWVKQRPEQGLEWIGWIDPENGDTEYASKFQDKATVTADTSSNTAYLQLSSLTSEDTAVYYCTLWLRRGLDYWGQGTSVTVSS (SEQ ID NO: 17) VLDIVMTQAAPSVPVTPGESVSISCRSSKSLLHSNGYTYLFWFLQRPGQSPQLLIYRMSNLASGVPDRFSGSGSGTAFTLRISRVEAEDVGVYYCMQHLEYPFTFGGGTKLEIK (SEQ ID NO: 18) 3-A4 CDR- GFNIKDDY (SEQ ID NO: DDYMY (SEQ ID NO: 7)GFNIKDD (SEQ ID N54T* H1 1) NO: 12) CDR- IDPETGDT (SEQ ID NO:WIDPETGDTEYASKFQD ETG (SEQ ID NO: H2 19) (SEQ ID NO: 20) 21) CDR-TLWLRRGLDY (SEQ ID WLRRGLDY (SEQ ID NO: 9) LRRGLD (SEQ ID H3 NO: 3)NO: 14) CDR- KSLLHSNGYTY (SEQ ID RSSKSLLHSNGYTYLF (SEQ SKSLLHSNGYTY L1NO: 4) ID NO: 10) (SEQ ID NO: 15) CDR- RMS (SEQ ID NO: 5)RMSNLAS (SEQ ID NO: 11) RMS(SEQ ID NO: L2 5) CDR- MQHLEYPFT (SEQ IDMQHLEYPFT (SEQ ID NO: 6) HLEYPF (SEQ ID L3 NO: 6) NO: 16) VHEVQLQQSGAELVRPGASVKLSCTASGFNIKDDYMYWVKQRPEQGLEWIGWIDPETGDTEYASKFQDKATVTADTSSNTAYLQLSSLTSEDTAVYYCTLWLRRGLDYWGQGTSVTVSS (SEQ ID NO: 22) VLDIVMTQAAPSVPVTPGESVSISCRSSKSLLHSNGYTYLFWFLQRPGQSPQLLIYRMSNLASGVPDRFSGSGSGTAFTLRISRVEAEDVGVYYCMQHLEYPFTFGGGTKLEIK (SEQ ID NO: 18) 3-A4 CDR- GFNIKDDY (SEQ ID NO: DDYMY (SEQ ID NO: 7)GFNIKDD (SEQ ID N54S* H1 1) NO: 12) CDR- IDPESGDT (SEQ ID NO:WIDPESGDTEYASKFQD ESG (SEQ ID NO: H2 23) (SEQ ID NO: 24) 25) CDR-TLWLRRGLDY (SEQ ID WLRRGLDY (SEQ ID NO: 9) LRRGLD (SEQ ID H3 NO: 3)NO: 14) CDR- KSLLHSNGYTY (SEQ ID RSSKSLLHSNGYTYLF (SEQ SKSLLHSNGYTY L1NO: 4) ID NO: 10) (SEQ ID NO: 15) CDR- RMS (SEQ ID NO: 5)RMSNLAS (SEQ ID NO: 11) RMS (SEQ ID NO: L2 5) CDR- MQHLEYPFT (SEQ IDMQHLEYPFT (SEQ ID NO: 6) HLEYPF (SEQ ID L3 NO: 6) NO: 16) VHEVQLQQSGAELVRPGASVKLSCTASGFNIKDDYMYWVKQRPEQGLEWIGWIDPESGDTEYASKFQDKATVTADTSSNTAYLQLSSLTSEDTAVYYCTLWLRRGLDYWGQGTSVTVSS (SEQ ID NO: 26) VLDIVMTQAAPSVPVTPGESVSISCRSSKSLLHSNGYTYLFWFLQRPGQSPQLLIYRMSNLASGVPDRFSGSGSGTAFTLRISRVEAEDVGVYYCMQHLEYPFTFGGGTKLEIK (SEQ ID NO: 18) 3-M12 CDR- GYSITSGYY (SEQ ID SGYYWN (SEQ ID NO: 33)GYSITSGY (SEQ H1 NO: 27) ID NO: 38) CDR- ITFDGAN (SEQ ID NO:YITFDGANNYNPSLKN (SEQ FDG (SEQ ID NO: H2 28) ID NO: 34) 39) CDR-TRSSYDYDVLDY (SEQ SSYDYDVLDY (SEQ ID NO: SYDYDVLD (SEQ H3 ID NO: 29) 35)ID NO: 40) CDR- QDISNF (SEQ ID NO: 30) RASQDISNFLN (SEQ ID NO:SQDISNF (SEQ ID L1 36) NO: 41) CDR- YTS (SEQ ID NO: 31)YTSRLHS (SEQ ID NO: 37) YTS (SEQ ID NO: L2 31) CDR- QQGHTLPYT (SEQ IDQQGHTLPYT (SEQ ID NO: 32) GHTLPY (SEQ ID L3 NO: 32) NO: 42) VHDVQLQESGPGLVKPSQSLSLTCSVTGYSITSGYYWNWIRQFPGNKLEWMGYITFDGANNYNPSLKNRISITRDTSKNQFFLKLTSVTTEDTATYYCTRSSYDYDVLDYWGQGTTLTVSS (SEQ ID NO: 43) VLDIQMTQTTSSLSASLGDRVTISCRASQDISNFLNWYQQRPDGTVKLLIYYTSRLHSGVPSRFSGSGSGTDFSLTVSNLEQEDIATYFCQQGHTLPYTFGGGTKLEIK (SEQ ID NO: 44)5-H12 CDR- GYSFTDYC (SEQ ID NO: DYCIN (SEQ ID NO: 51) GYSFTDY (SEQ ID H145) NO: 56) CDR- IYPGSGNT (SEQ ID NO: WIYPGSGNTRYSERFKG GSG (SEQ ID NO:H2 46) (SEQ ID NO: 52) 57) CDR- AREDYYPYHGMDY EDYYPYHGMDY (SEQ IDDYYPYHGMD H3 (SEQ ID NO: 47) NO: 53) (SEQ ID NO: 58) CDR-ESVDGYDNSF (SEQ ID RASESVDGYDNSFMH (SEQ SESVDGYDNSF Ll NO: 48)ID NO: 54) (SEQ ID NO: 59) CDR- RAS (SEQ ID NO: 49)RASNLES (SEQ ID NO: 55) RAS (SEQ ID NO: L2 49) CDR- QQSSEDPWT (SEQ IDQQSSEDPWT (SEQ ID NO: 50) SSEDPW (SEQ ID L3 NO: 50) NO: 60) VHQIQLQQSGPELVRPGASVKISCKASGYSFTDYCINWVNQRPGQGLEWIGWIYPGSGNTRYSERFKGKATLTVDTSSNTAYMQLSSLTSEDSAVYFCAREDYYPYHGMDYWGQGTSVTVSS (SEQ ID NO: 61) VLDIVLTQSPTSLAVSLGQRATISCRASESVDGYDNSFMHWYQQKPGQPPKLLIFRASNLESGIPARFSGSGSRTDFTLTINPVEAADVATYYCQQSSEDPWTFGGGTKLEIK (SEQ ID NO: 62) 5-H12 CDR- GYSFTDYY (SEQ ID DYYIN (SEQ ID NO: 64)GYSFTDY (SEQ ID C33Y* H1 NO: 63) NO: 56) CDR- IYPGSGNT (SEQ ID NO:WIYPGSGNTRYSERFKG GSG (SEQ ID NO: H2 46) (SEQ ID NO: 52) 57) CDR-AREDYYPYHGMDY EDYYPYHGMDY (SEQ ID DYYPYHGMD H3 (SEQ ID NO: 47) NO: 53)(SEQ ID NO: 58) CDR- ESVDGYDNSF (SEQ ID RASESVDGYDNSFMH (SEQ SESVDGYDNSFL1 NO: 48) ID NO: 54) (SEQ ID NO: 59) CDR- RAS (SEQ ID NO: 49)RASNLES (SEQ ID NO: 55) RAS (SEQ ID NO: L2 49) CDR- QQSSEDPWT (SEQ IDQQSSEDPWT (SEQ ID NO: 50) SSEDPW (SEQ ID L3 NO: 50) NO: 60) VHQIQLQQSGPELVRPGASVKISCKASGYSFTDYYINWVNQRPGQGLEWIGWIYPGSGNTRYSERFKGKATLTVDTSSNTAYMQLSSLTSEDSAVYFCAREDYYPYHGMDYWGQGTSVTVSS (SEQ ID NO: 65) VLDIVLTQSPTSLAVSLGQRATISCRASESVDGYDNSFMHWYQQKPGQPPKLLIFRASNLESGIPARFSGSGSRTDFTLTINPVEAADVATYYCQQSSEDPWTFGGGTKLEIK (SEQ ID NO: 62) 5-H12 CDR- GYSFTDYD (SEQ ID DYDIN (SEQ ID NO: 67)GYSFTDY (SEQ ID C33D* H1 NO: 66) NO: 56) CDR- IYPGSGNT (SEQ ID NO:WIYPGSGNTRYSERFKG GSG (SEQ ID NO: H2 46) (SEQ ID NO: 52) 57) CDR-AREDYYPYHGMDY EDYYPYHGMDY (SEQ ID DYYPYHGMD H3 (SEQ ID NO: 47) NO: 53)(SEQ ID NO: 58) CDR- ESVDGYDNSF (SEQ ID RASESVDGYDNSFMH (SEQ SESVDGYDNSFL1 NO: 48) ID NO: 54) (SEQ ID NO: 59) CDR- RAS (SEQ ID NO: 49)RASNLES (SEQ ID NO: 55) RAS (SEQ ID NO: L2 49) CDR- QQSSEDPWT (SEQ IDQQSSEDPWT (SEQ ID NO: 50) SSEDPW (SEQ ID L3 NO: 50) NO: 60) VHQIQLQQSGPELVRPGASVKISCKASGYSFTDYDINWVNQRPGQGLEWIGWIYPGS GNTRYSERFKGKATLTVDTSSNTAYMQLSSLTSEDSAVYFCAREDYYPYHGMDYWGQGTSVTVSS (SEQ ID NO: 68) VLDIVLTQSPTSLAVSLGQRATISCRASESVDGYDNSFMHWYQQKPGQPPKLLIFRASNLESGIPARFSGSGSRTDFTLTINPVEAADVATYYCQQSSEDPWTFGGGTKLEIK (SEQ ID NO: 62) *mutation positions are according to Kabat numberingof the respective VH sequences containing the mutations

In some embodiments, the anti-TfR antibody of the present disclosure isa humanized variant of any one of the anti-TfR antibodies provided inTable 2. In some embodiments, the anti-TfR antibody of the presentdisclosure comprises a CDR-H1, a CDR-H2, a CDR-H3, a CDR-L1, a CDR-L2,and a CDR-L3 that are the same as the CDR-H1, CDR-H2, and CDR-H3 in anyone of the anti-TfR antibodies provided in Table 2, and comprises ahumanized heavy chain variable region and/or (e.g., and) a humanizedlight chain variable region.

Humanized antibodies are human immunoglobulins (recipient antibody) inwhich residues from a complementarity determining region (CDR) of therecipient are replaced by residues from a CDR of a non-human species(donor antibody) such as mouse, rat, or rabbit having the desiredspecificity, affinity, and capacity. In some embodiments, Fv frameworkregion (FR) residues of the human immunoglobulin are replaced bycorresponding non-human residues. Furthermore, the humanized antibodymay comprise residues that are found neither in the recipient antibodynor in the imported CDR or framework sequences, but are included tofurther refine and optimize antibody performance. In general, thehumanized antibody will comprise substantially all of at least one, andtypically two, variable domains, in which all or substantially all ofthe CDR regions correspond to those of a non-human immunoglobulin andall or substantially all of the FR regions are those of a humanimmunoglobulin consensus sequence. The humanized antibody optimally alsowill comprise at least a portion of an immunoglobulin constant region ordomain (Fc), typically that of a human immunoglobulin. Antibodies mayhave Fc regions modified as described in WO 99/58572. Other forms ofhumanized antibodies have one or more CDRs (one, two, three, four, five,six) which are altered with respect to the original antibody, which arealso termed one or more CDRs derived from one or more CDRs from theoriginal antibody. Humanized antibodies may also involve affinitymaturation.

Humanized antibodies and methods of making them are known, e.g., asdescribed in Almagro et al., Front. Biosci. 13:1619-1633 (2008);Riechmann et al., Nature 332:323-329 (1988); Queen et al., Proc. Nat'lAcad. Sci. USA 86:10029-10033 (1989); U.S. Pat. Nos. 5,821,337,7,527,791, 6,982,321, and 7,087,409; Kashmiri et al., Methods 36:25-34(2005); Padlan et al., Mol. Immunol. 28:489-498 (1991); Dall'Acqua etal., Methods 36:43-60 (2005); Osbourn et al., Methods 36:61-68 (2005);and Klimka et al., Br. J. Cancer, 83:252-260 (2000), the contents of allof which are incorporated herein by reference. Human framework regionsthat may be used for humanization are described in e.g., Sims et al. J.Immunol. 151:2296 (1993); Carter et al., Proc. Natl. Acad. Sci. USA,89:4285 (1992); Presta et al., J. Immunol., 151:2623 (1993); Almagro etal., Front. Biosci. 13:1619-1633 (2008)); Baca et al., J. Biol. Chem.272:10678-10684 (1997); and Rosok et al., J Biol. Chem. 271:22611-22618(1996), the contents of all of which are incorporated herein byreference.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising one or more amino acidvariations (e.g., in the VH framework region) as compared with any oneof the VHs listed in Table 2, and/or (e.g., and) a humanized VLcomprising one or more amino acid variations (e.g., in the VL frameworkregion) as compared with any one of the VLs listed in Table 2.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH containing no more than 25 aminoacid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17,16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acidvariation) in the framework regions as compared with the VH of any ofthe anti-TfR antibodies listed in Table 2 (e.g., any one of SEQ ID NOs:17, 22, 26, 43, 61, 65, and 68). Alternatively or in addition (e.g., inaddition), the humanized anti-TfR antibody of the present disclosurecomprises a humanized VL containing no more than 25 amino acidvariations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16,15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acidvariation) in the framework regions as compared with the VL of any oneof the anti-TfR antibodies listed in Table 2 (e.g., any one of SEQ IDNOs: 18, 44, and 62).

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising an amino acid sequencethat is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%)identical in the framework regions to the VH of any of the anti-TfRantibodies listed in Table 2 (e.g., any one of SEQ ID NOs: 17, 22, 26,43, 61, 65, and 68). Alternatively or in addition (e.g., in addition),In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VL comprising an amino acid sequencethat is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%)identical in the framework regions to the VL of any of the anti-TfRantibodies listed in Table 2 (e.g., any one of SEQ ID NOs: 18, 44, and62).

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising a CDR-H1 having the aminoacid sequence of SEQ ID NO: 1 (according to the IMGT definition system),a CDR-H2 having the amino acid sequence of SEQ ID NO: 2, SEQ ID NO: 19,or SEQ ID NO: 23 (according to the IMGT definition system), a CDR-H3having the amino acid sequence of SEQ ID NO: 3 (according to the IMGTdefinition system), and containing no more than 25 amino acid variations(e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13,12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in theframework regions as compared with the VH as set forth in SEQ ID NO: 17,SEQ ID NO: 22, or SEQ ID NO: 26. Alternatively or in addition (e.g., inaddition), the anti-TfR antibody of the present disclosure comprises ahumanized VL comprising a CDR-L1 having the amino acid sequence of SEQID NO: 4 (according to the IMGT definition system), a CDR-L2 having theamino acid sequence of SEQ ID NO: 5 (according to the IMGT definitionsystem), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 6(according to the IMGT definition system), and containing no more than25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19,18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 aminoacid variation) in the framework regions as compared with the VL as setforth in SEQ ID NO: 18.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising a CDR-H1 having the aminoacid sequence of SEQ ID NO: 1 (according to the IMGT definition system),a CDR-H2 having the amino acid sequence of SEQ ID NO: 2, SEQ ID NO: 19,or SEQ ID NO: 23 (according to the IMGT definition system), a CDR-H3having the amino acid sequence of SEQ ID NO: 3 (according to the IMGTdefinition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%,98%, or 99%) identical in the framework regions to the VH as set forthin SEQ ID NO: 17, SEQ ID NO: 22, or SEQ ID NO: 26. Alternatively or inaddition (e.g., in addition), the humanized anti-TfR antibody of thepresent disclosure comprises a humanized VL comprising a CDR-L1 havingthe amino acid sequence of SEQ ID NO: 4 (according to the IMGTdefinition system), a CDR-L2 having the amino acid sequence of SEQ IDNO: 5 (according to the IMGT definition system), and a CDR-L3 having theamino acid sequence of SEQ ID NO: 6 (according to the IMGT definitionsystem), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or99%) identical in the framework regions to the VL as set forth in anyone of SEQ ID NO: 18.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising a CDR-H1 having the aminoacid sequence of SEQ ID NO: 7 (according to the Kabat definitionsystem), a CDR-H2 having the amino acid sequence of SEQ ID NO: 8, SEQ IDNO: 20, or SEQ ID NO: 24 (according to the Kabat definition system), aCDR-H3 having the amino acid sequence of SEQ ID NO: 9 (according to theKabat definition system), and containing no more than 25 amino acidvariations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16,15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acidvariation) in the framework regions as compared with the VH as set forthin SEQ ID NO: 17, SEQ ID NO: 22, or SEQ ID NO: 26. Alternatively or inaddition (e.g., in addition), the humanized anti-TfR antibody of thepresent disclosure comprises a humanized VL comprising a CDR-L1 havingthe amino acid sequence of SEQ ID NO: 10 (according to the Kabatdefinition system), a CDR-L2 having the amino acid sequence of SEQ IDNO: 11 (according to the Kabat definition system), and a CDR-L3 havingthe amino acid sequence of SEQ ID NO: 6 (according to the Kabatdefinition system), and containing no more than 25 amino acid variations(e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13,12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in theframework regions as compared with the VL as set forth in SEQ ID NO: 18.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising a CDR-H1 having the aminoacid sequence of SEQ ID NO: 7 (according to the Kabat definitionsystem), a CDR-H2 having the amino acid sequence of SEQ ID NO: 8, SEQ IDNO: 20, or SEQ ID NO: 24 (according to the Kabat definition system), aCDR-H3 having the amino acid sequence of SEQ ID NO: 9 (according to theKabat definition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%,95%, 98%, or 99%) identical in the framework regions to the VH as setforth in SEQ ID NO: 17, SEQ ID NO: 22, or SEQ ID NO: 26. Alternativelyor in addition (e.g., in addition), the humanized anti-TfR antibody ofthe present disclosure comprises a humanized VL comprising a CDR-L1having the amino acid sequence of SEQ ID NO: 10 (according to the Kabatdefinition system), a CDR-L2 having the amino acid sequence of SEQ IDNO: 11 (according to the Kabat definition system), and a CDR-L3 havingthe amino acid sequence of SEQ ID NO: 6 (according to the Kabatdefinition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%,98%, or 99%) identical in the framework regions to the VL as set forthin any one of SEQ ID NO: 18.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising a CDR-H1 having the aminoacid sequence of SEQ ID NO: 12 (according to the Chothia definitionsystem), a CDR-H2 having the amino acid sequence of SEQ ID NO: 13, SEQID NO: 21, or SEQ ID NO: 25 (according to the Chothia definitionsystem), a CDR-H3 having the amino acid sequence of SEQ ID NO: 14(according to the Chothia definition system), and containing no morethan 25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21,20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1amino acid variation) in the framework regions as compared with the VHas set forth in SEQ ID NO: 17, SEQ ID NO: 22 or SEQ ID NO: 26.Alternatively or in addition (e.g., in addition), the humanized anti-TfRantibody of the present disclosure comprises a humanized VL comprising aCDR-L1 having the amino acid sequence of SEQ ID NO: 15 (according to theChothia definition system), a CDR-L2 having the amino acid sequence ofSEQ ID NO: 5 (according to the Chothia definition system), and a CDR-L3having the amino acid sequence of SEQ ID NO: 16 (according to theChothia definition system), and containing no more than 25 amino acidvariations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16,15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acidvariation) in the framework regions as compared with the VL as set forthin SEQ ID NO: 18.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising a CDR-H1 having the aminoacid sequence of SEQ ID NO: 12 (according to the Chothia definitionsystem), a CDR-H2 having the amino acid sequence of SEQ ID NO: 13, SEQID NO: 21, or SEQ ID NO: 25 (according to the Chothia definitionsystem), a CDR-H3 having the amino acid sequence of SEQ ID NO: 14(according to the Chothia definition system), and is at least 75% (e.g.,75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regionsto the VH as set forth in SEQ ID NO: SEQ ID NO: 17, SEQ ID NO: 22 or SEQID NO: 26. Alternatively or in addition (e.g., in addition), theanti-TfR antibody of the present disclosure comprises a humanized VLcomprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 15(according to the Chothia definition system), a CDR-L2 having the aminoacid sequence of SEQ ID NO: 5 (according to the Chothia definitionsystem), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 16(according to the Chothia definition system), and is at least 75% (e.g.,75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regionsto the VL as set forth in any one of SEQ ID NO: 18.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising a CDR-H1 having the aminoacid sequence of SEQ ID NO: 27 (according to the IMGT definitionsystem), a CDR-H2 having the amino acid sequence of SEQ ID NO: 28(according to the IMGT definition system), a CDR-H3 having the aminoacid sequence of SEQ ID NO: 29 (according to the IMGT definitionsystem), and containing no more than 25 amino acid variations (e.g., nomore than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11,10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the frameworkregions as compared with the VH as set forth in SEQ ID NO: 43.Alternatively or in addition (e.g., in addition), the humanized anti-TfRantibody of the present disclosure comprises a humanized VL comprising aCDR-L1 having the amino acid sequence of SEQ ID NO: 30 (according to theIMGT definition system), a CDR-L2 having the amino acid sequence of SEQID NO: 31 (according to the IMGT definition system), and a CDR-L3 havingthe amino acid sequence of SEQ ID NO: 32 (according to the IMGTdefinition system), and containing no more than 25 amino acid variations(e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13,12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in theframework regions as compared with the VL as set forth in SEQ ID NO: 44.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising a CDR-H1 having the aminoacid sequence of SEQ ID NO: 27 (according to the IMGT definitionsystem), a CDR-H2 having the amino acid sequence of SEQ ID NO: 28(according to the IMGT definition system), a CDR-H3 having the aminoacid sequence of SEQ ID NO: 29 (according to the IMGT definitionsystem), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or99%) identical in the framework regions to the VH as set forth in SEQ IDNO: 43. Alternatively or in addition (e.g., in addition), the humanizedanti-TfR antibody of the present disclosure comprises a humanized VLcomprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 30(according to the IMGT definition system), a CDR-L2 having the aminoacid sequence of SEQ ID NO: 31 (according to the IMGT definitionsystem), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 32(according to the IMGT definition system), and is at least 75% (e.g.,75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regionsto the VL as set forth in SEQ ID NO: 44.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising a CDR-H1 having the aminoacid sequence of SEQ ID NO: 33 (according to the Kabat definitionsystem), a CDR-H2 having the amino acid sequence of SEQ ID NO: 34(according to the Kabat definition system), a CDR-H3 having the aminoacid sequence of SEQ ID NO: 35 (according to the Kabat definitionsystem), and containing no more than 25 amino acid variations (e.g., nomore than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11,10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the frameworkregions as compared with the VH as set forth in SEQ ID NO: 43.Alternatively or in addition (e.g., in addition), the humanized anti-TfRantibody of the present disclosure comprises a humanized VL comprising aCDR-L1 having the amino acid sequence of SEQ ID NO: 36 (according to theKabat definition system), a CDR-L2 having the amino acid sequence of SEQID NO: 37 (according to the Kabat definition system), and a CDR-L3having the amino acid sequence of SEQ ID NO: 32 (according to the Kabatdefinition system), and containing no more than 25 amino acid variations(e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13,12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in theframework regions as compared with the VL as set forth in SEQ ID NO: 44.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising a CDR-H1 having the aminoacid sequence of SEQ ID NO: 33 (according to the Kabat definitionsystem), a CDR-H2 having the amino acid sequence of SEQ ID NO: 34(according to the Kabat definition system), a CDR-H3 having the aminoacid sequence of SEQ ID NO: 35 (according to the Kabat definitionsystem), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or99%) identical in the framework regions to the VH as set forth in SEQ IDNO: 43. Alternatively or in addition (e.g., in addition), the humanizedanti-TfR antibody of the present disclosure comprises a humanized VLcomprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 36(according to the Kabat definition system), a CDR-L2 having the aminoacid sequence of SEQ ID NO: 37 (according to the Kabat definitionsystem), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 32(according to the Kabat definition system), and is at least 75% (e.g.,75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regionsto the VL as set forth in SEQ ID NO: 44.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising a CDR-H1 having the aminoacid sequence of SEQ ID NO: 38 (according to the Chothia definitionsystem), a CDR-H2 having the amino acid sequence of SEQ ID NO: 39(according to the Chothia definition system), a CDR-H3 having the aminoacid sequence of SEQ ID NO: 40 (according to the Chothia definitionsystem), and containing no more than 25 amino acid variations (e.g., nomore than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11,10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the frameworkregions as compared with the VH as set forth in SEQ ID NO: 43.Alternatively or in addition (e.g., in addition), the humanized anti-TfRantibody of the present disclosure comprises a humanized VL comprising aCDR-L1 having the amino acid sequence of SEQ ID NO: 41 (according to theChothia definition system), a CDR-L2 having the amino acid sequence ofSEQ ID NO: 31 (according to the Chothia definition system), and a CDR-L3having the amino acid sequence of SEQ ID NO: 42 (according to theChothia definition system), and containing no more than 25 amino acidvariations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16,15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acidvariation) in the framework regions as compared with the VL as set forthin SEQ ID NO: 44.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising a CDR-H1 having the aminoacid sequence of SEQ ID NO: 38 (according to the Chothia definitionsystem), a CDR-H2 having the amino acid sequence of SEQ ID NO: 39(according to the Chothia definition system), a CDR-H3 having the aminoacid sequence of SEQ ID NO: 40 (according to the Chothia definitionsystem), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or99%) identical in the framework regions to the VH as set forth in SEQ IDNO: 43. Alternatively or in addition (e.g., in addition), the humanizedanti-TfR antibody of the present disclosure comprises a humanized VLcomprising a CDR-L1 having the amino acid sequence of SEQ ID NO: 41(according to the Chothia definition system), a CDR-L2 having the aminoacid sequence of SEQ ID NO: 31 (according to the Chothia definitionsystem), and a CDR-L3 having the amino acid sequence of SEQ ID NO: 42(according to the Chothia definition system), and is at least 75% (e.g.,75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regionsto the VL as set forth in SEQ ID NO: 44.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising a CDR-H1 having the aminoacid sequence of SEQ ID NO: 45, SEQ ID NO: 63, or SEQ ID NO: 66(according to the IMGT definition system), a CDR-H2 having the aminoacid sequence of SEQ ID NO: 46 (according to the IMGT definitionsystem), a CDR-H3 having the amino acid sequence of SEQ ID NO: 47(according to the IMGT definition system), and containing no more than25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19,18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 aminoacid variation) in the framework regions as compared with the VH as setforth in SEQ ID NO: 61, SEQ ID NO: 65, or SEQ ID NO: 68. Alternativelyor in addition (e.g., in addition), the humanized anti-TfR antibody ofthe present disclosure comprises a humanized VL comprising a CDR-L1having the amino acid sequence of SEQ ID NO: 48 (according to the IMGTdefinition system), a CDR-L2 having the amino acid sequence of SEQ IDNO: 49 (according to the IMGT definition system), and a CDR-L3 havingthe amino acid sequence of SEQ ID NO: 50 (according to the IMGTdefinition system), and containing no more than 25 amino acid variations(e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13,12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in theframework regions as compared with the VL as set forth in SEQ ID NO: 62.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising a CDR-H1 having the aminoacid sequence of SEQ ID NO: 45, SEQ ID NO: 63, or SEQ ID NO: 66(according to the IMGT definition system), a CDR-H2 having the aminoacid sequence of SEQ ID NO: 46 (according to the IMGT definitionsystem), a CDR-H3 having the amino acid sequence of SEQ ID NO: 47(according to the IMGT definition system), and is at least 75% (e.g.,75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regionsto the VH as set forth in SEQ ID NO: 61, SEQ ID NO: 65, SEQ ID NO: 68.Alternatively or in addition (e.g., in addition), the humanized anti-TfRantibody of the present disclosure comprises a humanized VL comprising aCDR-L1 having the amino acid sequence of SEQ ID NO: 48 (according to theIMGT definition system), a CDR-L2 having the amino acid sequence of SEQID NO: 49 (according to the IMGT definition system), and a CDR-L3 havingthe amino acid sequence of SEQ ID NO: 50 (according to the IMGTdefinition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%,98%, or 99%) identical in the framework regions to the VL as set forthin SEQ ID NO: 62.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising a CDR-H1 having the aminoacid sequence of SEQ ID NO: 51, SEQ ID NO: 64, or SEQ ID NO: 67(according to the Kabat definition system), a CDR-H2 having the aminoacid sequence of SEQ ID NO: 52 (according to the Kabat definitionsystem), a CDR-H3 having the amino acid sequence of SEQ ID NO: 53(according to the Kabat definition system), and containing no more than25 amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19,18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 aminoacid variation) in the framework regions as compared with the VH as setforth in SEQ ID NO: 61, SEQ ID NO: 65, SEQ ID NO: 68. Alternatively orin addition (e.g., in addition), the humanized anti-TfR antibody of thepresent disclosure comprises a humanized VL comprising a CDR-L1 havingthe amino acid sequence of SEQ ID NO: 54 (according to the Kabatdefinition system), a CDR-L2 having the amino acid sequence of SEQ IDNO: 55 (according to the Kabat definition system), and a CDR-L3 havingthe amino acid sequence of SEQ ID NO: 50 (according to the Kabatdefinition system), and containing no more than 25 amino acid variations(e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13,12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in theframework regions as compared with the VL as set forth in SEQ ID NO: 62.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising a CDR-H1 having the aminoacid sequence of SEQ ID NO: 51, SEQ ID NO: 64, or SEQ ID NO: 67(according to the Kabat definition system), a CDR-H2 having the aminoacid sequence of SEQ ID NO: 52 (according to the Kabat definitionsystem), a CDR-H3 having the amino acid sequence of SEQ ID NO: 53(according to the Kabat definition system), and is at least 75% (e.g.,75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical in the framework regionsto the VH as set forth in SEQ ID NO: 61, SEQ ID NO: 65, SEQ ID NO: 68.Alternatively or in addition (e.g., in addition), the humanized anti-TfRantibody of the present disclosure comprises a humanized VL comprising aCDR-L1 having the amino acid sequence of SEQ ID NO: 54 (according to theKabat definition system), a CDR-L2 having the amino acid sequence of SEQID NO: 55 (according to the Kabat definition system), and a CDR-L3having the amino acid sequence of SEQ ID NO: 50 (according to the Kabatdefinition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%,98%, or 99%) identical in the framework regions to the VL as set forthin SEQ ID NO: 62.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising a CDR-H1 having the aminoacid sequence of SEQ ID NO: 56 (according to the Chothia definitionsystem), a CDR-H2 having the amino acid sequence of SEQ ID NO: 57(according to the Chothia definition system), a CDR-H3 having the aminoacid sequence of SEQ ID NO: 58 (according to the Chothia definitionsystem), and containing no more than 25 amino acid variations (e.g., nomore than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11,10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) in the frameworkregions as compared with the VH as set forth in SEQ ID NO: 61, SEQ IDNO: 65, SEQ ID NO: 68. Alternatively or in addition (e.g., in addition),the humanized anti-TfR antibody of the present disclosure comprises ahumanized VL comprising a CDR-L1 having the amino acid sequence of SEQID NO: 59 (according to the Chothia definition system), a CDR-L2 havingthe amino acid sequence of SEQ ID NO: 49 (according to the Chothiadefinition system), and a CDR-L3 having the amino acid sequence of SEQID NO: 60 (according to the Chothia definition system), and containingno more than 25 amino acid variations (e.g., no more than 25, 24, 23,22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3,2, or 1 amino acid variation) in the framework regions as compared withthe VL as set forth in SEQ ID NO: 62.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising a CDR-H1 having the aminoacid sequence of SEQ ID NO: 56 (according to the Chothia definitionsystem), a CDR-H2 having the amino acid sequence of SEQ ID NO: 57(according to the Chothia definition system), a CDR-H3 having the aminoacid sequence of SEQ ID NO: 58 (according to the Chothia definitionsystem), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or99%) identical in the framework regions to the VH as set forth in SEQ IDNO: 61, SEQ ID NO: 65, SEQ ID NO: 68. Alternatively or in addition(e.g., in addition), the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VL comprising a CDR-L1 having the aminoacid sequence of SEQ ID NO: 59 (according to the Chothia definitionsystem), a CDR-L2 having the amino acid sequence of SEQ ID NO: 49(according to the Chothia definition system), and a CDR-L3 having theamino acid sequence of SEQ ID NO: 60 (according to the Chothiadefinition system), and is at least 75% (e.g., 75%, 80%, 85%, 90%, 95%,98%, or 99%) identical in the framework regions to the VL as set forthin SEQ ID NO: 62.

Examples of amino acid sequences of the humanized anti-TfR antibodiesdescribed herein are provided in Table 3.

TABLE 3 Variable Regions of Humanized Anti-TfR Antibodies AntibodyVariable Region Amino Acid Sequence** 3A4 V_(H): VH3 (N54T*)/Vκ4EVQLVQSGSELKKPGASVKVSCTASGFNIKDDYMYWVRQPPGKGLEWIGWIDPETGDTEYASKFQDRVTVTADTSTNTAYMELSSLRSEDTAVYYCTLWLRRGLDYWGQGTLVTVSS (SEQ ID NO: 69) V_(L):DIVMTQSPLSLPVTPGEPASISCRSSKSLLHSNGYTYLFWFQQRPGQSPRLLIYRMSNLASGVPDRFSGSGSGTDFTLKISRVEAEDVGVYYCMQHLEYPFTFGGGTKVEIK (SEQ ID NO: 70) 3A4 V_(H): VH3 (N54S*)/Vκ4EVQLVQSGSELKKPGASVKVSCTASGFNIKDDYMYWVRQPPGKGLEWIGWIDPESGDTEYASKFQDRVTVTADTSTNTAYMELSSLRSEDTAVYYCTLWLRRGLDYWGQGTLVTVSS (SEQ ID NO: 71) V_(L):DIVMTQSPLSLPVTPGEPASISCRSSKSLLHSNGYTYLFWFQQRPGQSPRLLIYRMSNLASGVPDRFSGSGSGTDFTLKISRVEAEDVGVYYCMQHLEYPFTFGGGTKVEIK (SEQ ID NO: 70) 3A4 V_(H): VH3/Vκ4EVQLVQSGSELKKPGASVKVSCTASGFNIKDDYMYWVRQPPGKGLEWIGWIDPENGDTEYASKFQDRVTVTADTSTNTAYMELSSLRSEDTAVYYCTLWLRRGLDYWGQGTLVTVSS (SEQ ID NO: 72) V_(L):DIVMTQSPLSLPVTPGEPASISCRSSKSLLHSNGYTYLFWFQQRPGQSPRLLIYRMSNLASGVPDRFSGSGSGTDFTLKISRVEAEDVGVYYCMQHLEYPFTFGGGTKVEIK (SEQ ID NO: 70) 3M12 V_(H): VH3/Vκ2QVQLQESGPGLVKPSQTLSLTCSVTGYSITSGYYWNWIRQPPGKGLEWMGYITFDGANNYNPSLKNRVSISRDTSKNQFSLKLSSVTAEDTATYYCTRSSYDYDVLDYWGQGTTVTVSS (SEQ ID NO: 73) V_(L):DIQMTQSPSSLSASVGDRVTITCRASQDISNFLNWYQQKPGQPVKLLIYYTSRLHSGVPSRFSGSGSGTDFTLTISSLQPEDFATYFCQQGHTLPYTFGQGTKLEIK (SEQ ID NO: 74)3M12 V_(H): VH3/Vκ3QVQLQESGPGLVKPSQTLSLTCSVTGYSITSGYYWNWIRQPPGKGLEWMGYITFDGANNYNPSLKNRVSISRDTSKNQFSLKLSSVTAEDTATYYCTRSSYDYDVLDYWGQGTTVTVSS (SEQ ID NO: 73) V_(L):DIQMTQSPSSLSASVGDRVTITCRASQDISNFLNWYQQKPGQPVKLLIYYTSRLHSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQGHTLPYTFGQGTKLEIK (SEQ ID NO: 75)3M12 V_(H): VH4/Vκ2QVQLQESGPGLVKPSQTLSLTCTVTGYSITSGYYWNWIRQPPGKGLEWIGYITFDGANNYNPSLKNRVSISRDTSKNQFSLKLSSVTAEDTATYYCTRSSYDYDVLDYWGQGTTVTVSS (SEQ ID NO: 76) V_(L):DIQMTQSPSSLSASVGDRVTITCRASQDISNFLNWYQQKPGQPVKLLIYYTSRLHSGVPSRFSGSGSGTDFTLTISSLQPEDFATYFCQQGHTLPYTFGQGTKLEIK (SEQ ID NO: 74)3M12 V_(H): VH4/Vk3QVQLQESGPGLVKPSQTLSLTCTVTGYSITSGYYWNWIRQPPGKGLEWIGYITFDGANNYNPSLKNRVSISRDTSKNQFSLKLSSVTAEDTATYYCTRSSYDYDVLDYWGQGTTVTVSS (SEQ ID NO: 76) V_(L):DIQMTQSPSSLSASVGDRVTITCRASQDISNFLNWYQQKPGQPVKLLIYYTSRLHSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQGHTLPYTFGQGTKLEIK (SEQ ID NO: 75)5H12 V_(H): VH5 (C33Y*)/Vκ3QVQLVQSGAEVKKPGASVKVSCKASGYSFTDYYINWVRQAPGQGLEWMGWIYPGSGNTRYSERFKGRVTITRDTSASTAYMELSSLRSEDTAVYYCAREDYYPYHGMDYWGQGTLVTVSS (SEQ ID NO: 77) V_(L):DIVLTQSPDSLAVSLGERATINCRASESVDGYDNSFMHWYQQKPGQPPKLLIFRASNLESGVPDRFSGSGSRTDFTLTISSLQAEDVAVYYCQQSSEDPWTFGQGTKLEIK (SEQ ID NO: 78) 5H12 V_(H): VH5 (C33D*)/Vκ4QVQLVQSGAEVKKPGASVKVSCKASGYSFTDYDINWVRQAPGQGLEWMGWIYPGSGNTRYSERFKGRVTITRDTSASTAYMELSSLRSEDTAVYYCAREDYYPYHGMDYWGQGTLVTVSS (SEQ ID NO: 79) V_(L):DIVMTQSPDSLAVSLGERATINCRASESVDGYDNSFMHWYQQKPGQPPKLLIFRASNLESGVPDRFSGSGSGTDFTLTISSLQAEDVAVYYCQQSSEDPWTFGQGTKLEIK (SEQ ID NO: 80) 5H12 V_(H): VH5 (C33Y*)/Vκ4QVQLVQSGAEVKKPGASVKVSCKASGYSFTDYYINWVRQAPGQGLEWMGWIYPGSGNTRYSERFKGRVTITRDTSASTAYMELSSLRSEDTAVYYCAREDYYPYHGMDYWGQGTLVTVSS (SEQ ID NO: 77) V_(L):DIVMTQSPDSLAVSLGERATINCRASESVDGYDNSFMHWYQQKPGQPPKLLIFRASNLESGVPDRFSGSGSGTDFTLTISSLQAEDVAVYYCQQSSEDPWTFGQGTKLEIK (SEQ ID NO: 80) *mutation positions are according to Kabat numberingof the respective VH sequences containing the mutations ** CDRsaccording to the Kabat numbering system are bolded

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising the CDR-H1, CDR-H2, andCDR-H3 of any one of the anti-TfR antibodies provided in Table 2 andcomprises one or more (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more)amino acid variations in the framework regions as compared with therespective humanized VH provided in Table 3. Alternatively or inaddition (e.g., in addition), the humanized anti-TfR antibody of thepresent disclosure comprises a humanized VL comprising the CDR-L1,CDR-L2, and CDR-L3 of any one of the anti-TfR antibodies provided inTable 2 and comprises one or more (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10or more) amino acid variations in the framework regions as compared withthe respective humanized VL provided in Table 3.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 69, and/or (e.g., and) a humanized VL comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 70. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a humanized VHcomprising the amino acid sequence of SEQ ID NO: 69 and a humanized VLcomprising the amino acid sequence of SEQ ID NO: 70.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 71, and/or (e.g., and) a humanized VL comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 70. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a humanized VHcomprising the amino acid sequence of SEQ ID NO: 71 and a humanized VLcomprising the amino acid sequence of SEQ ID NO: 70.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 72, and/or (e.g., and) a humanized VL comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 70. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a humanized VHcomprising the amino acid sequence of SEQ ID NO: 72 and a humanized VLcomprising the amino acid sequence of SEQ ID NO: 70.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 73, and/or (e.g., and) a humanized VL comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 74. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a humanized VHcomprising the amino acid sequence of SEQ ID NO: 73 and a humanized VLcomprising the amino acid sequence of SEQ ID NO: 74.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 73, and/or (e.g., and) a humanized VL comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 75. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a humanized VHcomprising the amino acid sequence of SEQ ID NO: 73 and a humanized VLcomprising the amino acid sequence of SEQ ID NO: 75.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 76, and/or (e.g., and) a humanized VL comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 74. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a humanized VHcomprising the amino acid sequence of SEQ ID NO: 76 and a humanized VLcomprising the amino acid sequence of SEQ ID NO: 74.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 76, and/or (e.g., and) a humanized VL comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 75. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a humanized VHcomprising the amino acid sequence of SEQ ID NO: 76 and a humanized VLcomprising the amino acid sequence of SEQ ID NO: 75.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 77, and/or (e.g., and) a humanized VL comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 78. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a humanized VHcomprising the amino acid sequence of SEQ ID NO: 77 and a humanized VLcomprising the amino acid sequence of SEQ ID NO: 78.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 79, and/or (e.g., and) a humanized VL comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 80. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a humanized VHcomprising the amino acid sequence of SEQ ID NO: 79 and a humanized VLcomprising the amino acid sequence of SEQ ID NO: 80.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a humanized VH comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 77, and/or (e.g., and) a humanized VL comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 80. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a humanized VHcomprising the amino acid sequence of SEQ ID NO: 77 and a humanized VLcomprising the amino acid sequence of SEQ ID NO: 80.

In some embodiments, the humanized anti-TfR antibody described herein isa full-length IgG, which can include a heavy constant region and a lightconstant region from a human antibody. In some embodiments, the heavychain of any of the anti-TfR antibodies as described herein maycomprises a heavy chain constant region (CH) or a portion thereof (e.g.,CH1, CH2, CH3, or a combination thereof). The heavy chain constantregion can of any suitable origin, e.g., human, mouse, rat, or rabbit.In one specific example, the heavy chain constant region is from a humanIgG (a gamma heavy chain), e.g., IgG1, IgG2, or IgG4. An example of ahuman IgG1 constant region is given below:

(SEQ ID NO: 81) ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPG  K

In some embodiments, the heavy chain of any of the anti-TfR antibodiesdescribed herein comprises a mutant human IgG1 constant region. Forexample, the introduction of LALA mutations (a mutant derived from mAbb12 that has been mutated to replace the lower hinge residues Leu234Leu235 with Ala234 and Ala235) in the CH2 domain of human IgG1 is knownto reduce Fcg receptor binding (Bruhns, P., et al. (2009) and Xu, D. etal. (2000)). The mutant human IgG1 constant region is provided below(mutations bonded and underlined):

(SEQ ID NO: 82) ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKV DKKVEPKSCDKTHTCPPCPAPEAA GGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPG K

In some embodiments, the light chain of any of the anti-TfR antibodiesdescribed herein may further comprise a light chain constant region(CL), which can be any CL known in the art. In some examples, the CL isa kappa light chain. In other examples, the CL is a lambda light chain.In some embodiments, the CL is a kappa light chain, the sequence ofwhich is provided below:

(SEQ ID NO: 83) RTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGL  SSPVTKSFNRGEC

Other antibody heavy and light chain constant regions are well known inthe art, e.g., those provided in the IMGT database (www.imgt.org) or atwww.vbase2.org/vbstat.php., both of which are incorporated by referenceherein.

In some embodiments, the humanized anti-TfR antibody described hereincomprises a heavy chain comprising any one of the VH as listed in Table3 or any variants thereof and a heavy chain constant region that is atleast 80%, at least 85%, at least 90%, at least 95%, or at least 99%identical to SEQ ID NO: 81 or SEQ ID NO: 82. In some embodiments, thehumanized anti-TfR antibody described herein comprises a heavy chaincomprising any one of the VH as listed in Table 3 or any variantsthereof and a heavy chain constant region that contains no more than 25amino acid variations (e.g., no more than 25, 24, 23, 22, 21, 20, 19,18, 17, 16, 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 aminoacid variation) as compared with SEQ ID NO: 81 or SEQ ID NO: 82. In someembodiments, the humanized anti-TfR antibody described herein comprisesa heavy chain comprising any one of the VH as listed in Table 3 or anyvariants thereof and a heavy chain constant region as set forth in SEQID NO: 81. In some embodiments, the humanized anti-TfR antibodydescribed herein comprises heavy chain comprising any one of the VH aslisted in Table 3 or any variants thereof and a heavy chain constantregion as set forth in SEQ ID NO: 82.

In some embodiments, the humanized anti-TfR antibody described hereincomprises a light chain comprising any one of the VL as listed in Table3 or any variants thereof and a light chain constant region that is atleast 80%, at least 85%, at least 90%, at least 95%, or at least 99%identical to SEQ ID NO: 83. In some embodiments, the humanized anti-TfRantibody described herein comprises a light chain comprising any one ofthe VL as listed in Table 3 or any variants thereof and a light chainconstant region contains no more than 25 amino acid variations (e.g., nomore than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11,10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) as compared withSEQ ID NO: 83. In some embodiments, the humanized anti-TfR antibodydescribed herein comprises a light chain comprising any one of the VL aslisted in Table 3 or any variants thereof and a light chain constantregion set forth in SEQ ID NO: 83.

Examples of IgG heavy chain and light chain amino acid sequences of theanti-TfR antibodies described are provided in Table 4 below.

TABLE 4Heavy chain and light chain sequences of examples of humanized anti-TfR IgGsAntibody IgG Heavy Chain/Light Chain Sequences** 3A4Heavy Chain (with wild type human IgG1 constant region) VH3 (N54T*)/Vκ4EVQLVQSGSELKKPGASVKVSCTASGFNIKDDYMYWVRQPPGKGLEWIGWIDPETGDTEYASKFQDRVTVTADTSTNTAYMELSSLRSEDTAVYYCTLWLRRGLDYWGQGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 84)Light Chain (with kappa light chain constant region)DIVMTQSPLSLPVTPGEPASISCRSSKSLLHSNGYTYLFWFQQRPGQSPRLLIYRMSNLASGVPDRFSGSGSGTDFTLKISRVEAEDVGVYYCMQHLEYPFTFGGGTKVEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 85) 3A4Heavy Chain (with wild type human IgG1 constant region) VH3 (N54S*)/Vκ4EVQLVQSGSELKKPGASVKVSCTASGFNIKDDYMYWVRQPPGKGLEWIGWIDPESGDTEYASKFQDRVTVTADTSTNTAYMELSSLRSEDTAVYYCTLWLRRGLDYWGQGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 86)Light Chain (with kappa light chain constant region)DIVMTQSPLSLPVTPGEPASISCRSSKSLLHSNGYTYLFWFQQRPGQSPRLLIYRMSNLASGVPDRFSGSGSGTDFTLKISRVEAEDVGVYYCMQHLEYPFTFGGGTKVEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 85) 3A4Heavy Chain (with wild type human IgG1 constant region) VH3/Vκ4EVQLVQSGSELKKPGASVKVSCTASGFNIKDDYMYWVRQPPGKGLEWIGWIDPENGDTEYASKFQDRVTVTADTSTNTAYMELSSLRSEDTAVYYCTLWLRRGLDYWGQGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 87)Light Chain (with kappa light chain constant region)DIVMTQSPLSLPVTPGEPASISCRSSKSLLHSNGYTYLFWFQQRPGQSPRLLIYRMSNLASGVPDRFSGSGSGTDFTLKISRVEAEDVGVYYCMQHLEYPFTFGGGTKVEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 85)3M12 Heavy Chain (with wild type human IgG1 constant region) VH3/Vκ2QVQLQESGPGLVKPSQTLSLTCSVTGYSITSGYYWNWIRQPPGKGLEWMGYITFDGANNYNPSLKNRVSISRDTSKNQFSLKLSSVTAEDTATYYCTRSSYDYDVLDYWGQGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 88)Light Chain (with kappa light chain constant region)DIQMTQSPSSLSASVGDRVTITCRASQDISNFLNWYQQKPGQPVKLLIYYTSRLHSGVPSRFSGSGSGTDFTLTISSLQPEDFATYFCQQGHTLPYTFGQGTKLEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 89) 3M12Heavy Chain (with wild type human IgG1 constant region) VH3/Vκ3QVQLQESGPGLVKPSQTLSLTCSVTGYSITSGYYWNWIRQPPGKGLEWMGYITFDGANNYNPSLKNRVSISRDTSKNQFSLKLSSVTAEDTATYYCTRSSYDYDVLDYWGQGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 88)Light Chain (with kappa light chain constant region)DIQMTQSPSSLSASVGDRVTITCRASQDISNFLNWYQQKPGQPVKLLIYYTSRLHSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQGHTLPYTFGQGTKLEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 90) 3M12Heavy Chain (with wild type human IgG1 constant region) VH4/Vκ2QVQLQESGPGLVKPSQTLSLTCTVTGYSITSGYYWNWIRQPPGKGLEWIGYITFDGANNYNPSLKNRVSISRDTSKNQFSLKLSSVTAEDTATYYCTRSSYDYDVLDYWGQGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 91)Light Chain (with kappa light chain constant region)DIQMTQSPSSLSASVGDRVTITCRASQDISNFLNWYQQKPGQPVKLLIYYTSRLHSGVPSRFSGSGSGTDFTLTISSLQPEDFATYFCQQGHTLPYTFGQGTKLEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 89) 3M12Heavy Chain (with wild type human IgG1 constant region) VH4/Vκ3QVQLQESGPGLVKPSQTLSLTCTVTGYSITSGYYWNWIRQPPGKGLEWIGYITFDGANNYNPSLKNRVSISRDTSKNQFSLKLSSVTAEDTATYYCTRSSYDYDVLDYWGQGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 91)Light Chain (with kappa light chain constant region)DIQMTQSPSSLSASVGDRVTITCRASQDISNFLNWYQQKPGQPVKLLIYYTSRLHSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQGHTLPYTFGQGTKLEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 90) 5H12Heavy Chain (with wild type human IgG1 constant region) VH5 (C33Y*)/Vκ3QVQLVQSGAEVKKPGASVKVSCKASGYSFTDYYINWVRQAPGQGLEWMGWIYPGSGNTRYSERFKGRVTITRDTSASTAYMELSSLRSEDTAVYYCAREDYYPYHGMDYWGQGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 92)Light Chain (with kappa light chain constant region)DIVLTQSPDSLAVSLGERATINCRASESVDGYDNSFMHWYQQKPGQPPKLLIFRASNLESGVPDRFSGSGSRTDFTLTISSLQAEDVAVYYCQQSSEDPWTFGQGTKLEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 93) 5H12Heavy Chain (with wild type human IgG1 constant region) VH5 (C33D*)/Vκ4QVQLVQSGAEVKKPGASVKVSCKASGYSFTDYDINWVRQAPGQGLEWMGWIYPGSGNTRYSERFKGRVTITRDTSASTAYMELSSLRSEDTAVYYCAREDYYPYHGMDYWGQGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 94)Light Chain (with kappa light chain constant region)DIVMTQSPDSLAVSLGERATINCRASESVDGYDNSFMHWYQQKPGQPPKLLIFRASNLESGVPDRFSGSGSGTDFTLTISSLQAEDVAVYYCQQSSEDPWTFGQGTKLEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 95)5H12 Heavy Chain (with wild type human IgG1 constant region)VH5 (C33Y*)/Vκ4 QVQLVQSGAEVKKPGASVKVSCKASGYSFTDYYINWVRQAPGQGLEWMGWIYPGSGNTRYSERFKGRVTITRDTSASTAYMELSSLRSEDTAVYYCAREDYYPYHGMDYWGQGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK (SEQ ID NO: 92)Light Chain (with kappa light chain constant region)DIVMTQSPDSLAVSLGERATINCRASESVDGYDNSFMHWYQQKPGQPPKLLIFRASNLESGVPDRFSGSGSGTDFTLTISSLQAEDVAVYYCQQSSEDPWTFGQGTKLEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 95)*mutation positions are according to Kabat numbering of the respectiveVH sequences containing the mutations **CDRs according to the Kabatnumbering system are bolded; VH/VL sequences underlined

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain containing no more than 25 amino acidvariations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16,15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acidvariation) as compared with the heavy chain as set forth in any one ofSEQ ID NOs: 84, 86, 87, 88, 91, 92, and 94. Alternatively or in addition(e.g., in addition), the humanized anti-TfR antibody of the presentdisclosure comprises a light chain containing no more than 25 amino acidvariations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16,15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acidvariation) as compared with the light chain as set forth in any one ofSEQ ID NOs: 85, 89, 90, 93, and 95.

In some embodiments, the humanized anti-TfR antibody described hereincomprises a heavy chain comprising an amino acid sequence that is atleast 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical to anyone of SEQ ID NOs: 84, 86, 87, 88, 91, 92, and 94. Alternatively or inaddition (e.g., in addition), the humanized anti-TfR antibody describedherein comprises a light chain comprising an amino acid sequence that isat least 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical toany one of SEQ ID NOs: 85, 89, 90, 93, and 95. In some embodiments, theanti-TfR antibody described herein comprises a heavy chain comprisingthe amino acid sequence of any one of SEQ ID NOs: 84, 86, 87, 88, 91,92, and 94. Alternatively or in addition (e.g., in addition), theanti-TfR antibody described herein comprises a light chain comprisingthe amino acid sequence of any one of SEQ ID NOs: 85, 89, 90, 93, and95.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 84, and/or (e.g., and) a light chain comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 85. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 84 and a light chaincomprising the amino acid sequence of SEQ ID NO: 85.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 86, and/or (e.g., and) a light chain comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 85. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 86 and a light chaincomprising the amino acid sequence of SEQ ID NO: 85.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 87, and/or (e.g., and) a light chain comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 85. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 87 and a light chaincomprising the amino acid sequence of SEQ ID NO: 85.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 88, and/or (e.g., and) a light chain comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 89. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 88 and a light chaincomprising the amino acid sequence of SEQ ID NO: 89.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 88, and/or (e.g., and) a light chain comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 90. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 88 and a light chaincomprising the amino acid sequence of SEQ ID NO: 90.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 91, and/or (e.g., and) a light chain comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 89. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 91 and a light chaincomprising the amino acid sequence of SEQ ID NO: 89.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 91, and/or (e.g., and) a light chain comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 90. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 91 and a light chaincomprising the amino acid sequence of SEQ ID NO: 90.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 92, and/or (e.g., and) a light chain comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 93. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 92 and a light chaincomprising the amino acid sequence of SEQ ID NO: 93.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 94, and/or (e.g., and) a light chain comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 95. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 94 and a light chaincomprising the amino acid sequence of SEQ ID NO: 95.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 92, and/or (e.g., and) a light chain comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 95. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 92 and a light chaincomprising the amino acid sequence of SEQ ID NO: 95.

In some embodiments, the anti-TfR antibody is a Fab fragment, Fab′fragment, or F(ab′)2 fragment of an intact antibody (full-lengthantibody). Antigen binding fragment of an intact antibody (full-lengthantibody) can be prepared via routine methods (e.g., recombinantly or bydigesting the heavy chain constant region of a full length IgG using anenzyme such as papain). For example, F(ab′)2 fragments can be producedby pepsin or papain digestion of an antibody molecule, and Fab′fragments that can be generated by reducing the disulfide bridges ofF(ab′)2 fragments. In some embodiments, a heavy chain constant region ina Fab fragment of the anti-TfR1 antibody described herein comprises theamino acid sequence of:

(SEQ ID NO: 96) ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEP KSCDKTHT

In some embodiments, the humanized anti-TfR antibody described hereincomprises a heavy chain comprising any one of the VH as listed in Table3 or any variants thereof and a heavy chain constant region that is atleast 80%, at least 85%, at least 90%, at least 95%, or at least 99%identical to SEQ ID NO: 96. In some embodiments, the humanized anti-TfRantibody described herein comprises a heavy chain comprising any one ofthe VH as listed in Table 3 or any variants thereof and a heavy chainconstant region that contains no more than 25 amino acid variations(e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13,12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) ascompared with SEQ ID NO: 96. In some embodiments, the humanized anti-TfRantibody described herein comprises a heavy chain comprising any one ofthe VH as listed in Table 3 or any variants thereof and a heavy chainconstant region as set forth in SEQ ID NO: 96.

In some embodiments, the humanized anti-TfR antibody described hereincomprises a light chain comprising any one of the VL as listed in Table3 or any variants thereof and a light chain constant region that is atleast 80%, at least 85%, at least 90%, at least 95%, or at least 99%identical to SEQ ID NO: 83. In some embodiments, the humanized anti-TfRantibody described herein comprises a light chain comprising any one ofthe VL as listed in Table 3 or any variants thereof and a light chainconstant region contains no more than 25 amino acid variations (e.g., nomore than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11,10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) as compared withSEQ ID NO: 83. In some embodiments, the humanized anti-TfR antibodydescribed herein comprises a light chain comprising any one of the VL aslisted in Table 3 or any variants thereof and a light chain constantregion set forth in SEQ ID NO: 83.

Examples of Fab heavy chain and light chain amino acid sequences of theanti-TfR antibodies described are provided in Table 5 below.

TABLE 5 Heavy chain and light chain sequences of examples ofhumanized anti-TfR Fabs Antibody Fab Heavy Chain/Light Chain Sequences**3A4 VH3 Heavy Chain (with partial human IgG1 constant region)(N54T*)/Vκ4 EVQLVQSGSELKKPGASVKVSCTASGFNIKDDYMYWVRQPPGKGLEWIGWIDPETGDTEYASKFQDRVTVTADTSTNTAYMELSSLRSEDTAVYYCTLWLRRGLDYWGQGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHT (SEQ ID NO: 97)Light Chain (with kappa light chain constant region)DIVMTQSPLSLPVTPGEPASISCRSSKSLLHSNGYTYLFWFQQRPGQSPRLLIYRMSNLASGVPDRFSGSGSGTDFTLKISRVEAEDVGVYYCMQHLEYPFTFGGGTKVEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 85) 3A4 VH3Heavy Chain (with partial human IgG1 constant region) (N54S*)/Vκ4EVQLVQSGSELKKPGASVKVSCTASGFNIKDDYMYWVRQPPGKGLEWIGWIDPESGDTEYASKFQDRVTVTADTSTNTAYMELSSLRSEDTAVYYCTLWLRRGLDYWGQGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHT (SEQ ID NO: 98)Light Chain (with kappa light chain constant region)DIVMTQSPLSLPVTPGEPASISCRSSKSLLHSNGYTYLFWFQQRPGQSPRLLIYRMSNLASGVPDRFSGSGSGTDFTLKISRVEAEDVGVYYCMQHLEYPFTFGGGTKVEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 85) 3A4Heavy Chain (with partial human IgG1 constant region) VH3/Vκ4EVQLVQSGSELKKPGASVKVSCTASGFNIKDDYMYWVRQPPGKGLEWIGWIDPENGDTEYASKFQDRVTVTADTSTNTAYMELSSLRSEDTAVYYCTLWLRRGLDYWGQGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHT (SEQ ID NO: 99)Light Chain (with kappa light chain constant region)DIVMTQSPLSLPVTPGEPASISCRSSKSLLHSNGYTYLFWFQQRPGQSPRLLIYRMSNLASGVPDRFSGSGSGTDFTLKISRVEAEDVGVYYCMQHLEYPFTFGGGTKVEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 85) 3M12Heavy Chain (with partial human IgG1 constant region) VH3/Vκ2QVQLQESGPGLVKPSQTLSLTCSVTGYSITSGYYWNWIRQPPGKGLEWMGYITFDGANNYNPSLKNRVSISRDTSKNQFSLKLSSVTAEDTATYYCTRSSYDYDVLDYWGQGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHT (SEQ ID NO: 100)Light Chain (with kappa light chain constant region)DIQMTQSPSSLSASVGDRVTITCRASQDISNFLNWYQQKPGQPVKLLIYYTSRLHSGVPSRFSGSGSGTDFTLTISSLQPEDFATYFCQQGHTLPYTFGQGTKLEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 89)3M12 Heavy Chain (with partial human IgG1 constant region) VH3/Vκ3QVQLQESGPGLVKPSQTLSLTCSVTGYSITSGYYWNWIRQPPGKGLEWMGYITFDGANNYNPSLKNRVSISRDTSKNQFSLKLSSVTAEDTATYYCTRSSYDYDVLDYWGQGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHT (SEQ ID NO: 100)Light Chain (with kappa light chain constant region)DIQMTQSPSSLSASVGDRVTITCRASQDISNFLNWYQQKPGQPVKLLIYYTSRLHSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQGHTLPYTFGQGTKLEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 90)3M12 Heavy Chain (with partial human IgG1 constant region) VH4/Vκ2QVQLQESGPGLVKPSQTLSLTCTVTGYSITSGYYWNWIRQPPGKGLEWIGYITFDGANNYNPSLKNRVSISRDTSKNQFSLKLSSVTAEDTATYYCTRSSYDYDVLDYWGQGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHT (SEQ ID NO: 101)Light Chain (with kappa light chain constant region)DIQMTQSPSSLSASVGDRVTITCRASQDISNFLNWYQQKPGQPVKLLIYYTSRLHSGVPSRFSGSGSGTDFTLTISSLQPEDFATYFCQQGHTLPYTFGQGTKLEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 89)3M12 Heavy Chain (with partial human IgG1 constant region) VH4/Vκ3QVQLQESGPGLVKPSQTLSLTCTVTGYSITSGYYWNWIRQPPGKGLEWIGYITFDGANNYNPSLKNRVSISRDTSKNQFSLKLSSVTAEDTATYYCTRSSYDYDVLDYWGQGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHT (SEQ ID NO: 101)Light Chain (with kappa light chain constant region)DIQMTQSPSSLSASVGDRVTITCRASQDISNFLNWYQQKPGQPVKLLIYYTSRLHSGVPSRFSGSGSGTDFTLTISSLQPEDFATYYCQQGHTLPYTFGQGTKLEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 90)5H12 VH5 Heavy Chain (with partial human IgG1 constant region)(C33Y*)/Vκ3 QVQLVQSGAEVKKPGASVKVSCKASGYSFTDYYINWVRQAPGQGLEWMGWIYPGSGNTRYSERFKGRVTITRDTSASTAYMELSSLRSEDTAVYYCAREDYYPYHGMDYWGQGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHT (SEQ ID NO: 102)Light Chain (with kappa light chain constant region)DIVLTQSPDSLAVSLGERATINCRASESVDGYDNSFMHWYQQKPGQPPKLLIFRASNLESGVPDRFSGSGSRTDFTLTISSLQAEDVAVYYCQQSSEDPWTFGQGTKLEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 93) 5H12 VH5Heavy Chain (with partial human IgG1 constant region) (C33D*)/Vκ4QVQLVQSGAEVKKPGASVKVSCKASGYSFTDYDINWVRQAPGQGLEWMGWIYPGSGNTRYSERFKGRVTITRDTSASTAYMELSSLRSEDTAVYYCAREDYYPYHGMDYWGQGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHT (SEQ ID NO: 103)Light Chain (with kappa light chain constant region)DIVMTQSPDSLAVSLGERATINCRASESVDGYDNSFMHWYQQKPGQPPKLLIFRASNLESGVPDRFSGSGSGTDFTLTISSLQAEDVAVYYCQQSSEDPWTFGQGTKLEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 95) 5H12 VH5Heavy Chain (with partial human IgG1 constant region) (C33Y*)/Vκ4QVQLVQSGAEVKKPGASVKVSCKASGYSFTDYYINWVRQAPGQGLEWMGWIYPGSGNTRYSERFKGRVTITRDTSASTAYMELSSLRSEDTAVYYCAREDYYPYHGMDYWGQGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHT (SEQ ID NO: 102)Light Chain (with kappa light chain constant region)DIVMTQSPDSLAVSLGERATINCRASESVDGYDNSFMHWYQQKPGQPPKLLIFRASNLESGVPDRFSGSGSGTDFTLTISSLQAEDVAVYYCQQSSEDPWTFGQGTKLEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTKSFNRGEC (SEQ ID NO: 95) *mutation positions are according to Kabat numberingof the respective VH sequences containing the mutations **CDRs accordingto the Kabat numbering system are bolded; VH/VL sequences underlined

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain containing no more than 25 amino acidvariations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16,15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acidvariation) as compared with the heavy chain as set forth in any one ofSEQ ID NOs: 97-103. Alternatively or in addition (e.g., in addition),the humanized anti-TfR antibody of the present disclosure comprises alight chain containing no more than 25 amino acid variations (e.g., nomore than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15, 14, 13, 12, 11,10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acid variation) as compared withthe light chain as set forth in any one of SEQ ID NOs: 85, 89, 90, 93,and 95.

In some embodiments, the humanized anti-TfR antibody described hereincomprises a heavy chain comprising an amino acid sequence that is atleast 75% (e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical to anyone of SEQ ID NOs: 97-103. Alternatively or in addition (e.g., inaddition), the humanized anti-TfR antibody described herein comprises alight chain comprising an amino acid sequence that is at least 75%(e.g., 75%, 80%, 85%, 90%, 95%, 98%, or 99%) identical to any one of SEQID NOs: 85, 89, 90, 93, and 95. In some embodiments, the anti-TfRantibody described herein comprises a heavy chain comprising the aminoacid sequence of any one of SEQ ID NOs: 97-103. Alternatively or inaddition (e.g., in addition), the anti-TfR antibody described hereincomprises a light chain comprising the amino acid sequence of any one ofSEQ ID NOs: 85, 89, 90, 93, and 95.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 97, and/or (e.g., and) a light chain comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 85. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 97 and a light chaincomprising the amino acid sequence of SEQ ID NO: 85.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 98, and/or (e.g., and) a light chain comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 85. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 98 and a light chaincomprising the amino acid sequence of SEQ ID NO: 85.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 99, and/or (e.g., and) a light chain comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 85. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 99 and a light chaincomprising the amino acid sequence of SEQ ID NO: 85.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 100, and/or (e.g., and) a light chain comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 89. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 100 and a light chaincomprising the amino acid sequence of SEQ ID NO: 89.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 100, and/or (e.g., and) a light chain comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 90. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 100 and a light chaincomprising the amino acid sequence of SEQ ID NO: 90.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 101, and/or (e.g., and) a light chain comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 89. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 101 and a light chaincomprising the amino acid sequence of SEQ ID NO: 89.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 101, and/or (e.g., and) a light chain comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 90. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 101 and a light chaincomprising the amino acid sequence of SEQ ID NO: 90.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 102, and/or (e.g., and) a light chain comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 93. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 102 and a light chaincomprising the amino acid sequence of SEQ ID NO: 93.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 103, and/or (e.g., and) a light chain comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 95. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 103 and a light chaincomprising the amino acid sequence of SEQ ID NO: 95.

In some embodiments, the humanized anti-TfR antibody of the presentdisclosure comprises a heavy chain comprising an amino acid sequencethat is at least 80% (e.g., 80%, 85%, 90%, 95%, 98%, or 99%) identicalto SEQ ID NO: 102, and/or (e.g., and) a light chain comprising an aminoacid sequence that is at least 80% identical (e.g., 80%, 85%, 90%, 95%,98%, or 99%) to SEQ ID NO: 95. In some embodiments, the humanizedanti-TfR antibody of the present disclosure comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 102 and a light chaincomprising the amino acid sequence of SEQ ID NO: 95.

In some embodiments, the humanized anti-TfR receptor antibodiesdescribed herein can be in any antibody form, including, but not limitedto, intact (i.e., full-length) antibodies, antigen-binding fragmentsthereof (such as Fab, Fab′, F(ab′)2, Fv), single chain antibodies,bi-specific antibodies, or nanobodies. In some embodiments, humanizedthe anti-TfR antibody described herein is a scFv. In some embodiments,the humanized anti-TfR antibody described herein is a scFv-Fab (e.g.,scFv fused to a portion of a constant region). In some embodiments, theanti-TfR receptor antibody described herein is a scFv fused to aconstant region (e.g., human IgG1 constant region as set forth in SEQ IDNO: 81 or SEQ ID NO: 82, or a portion thereof such as the Fc portion) ateither the N-terminus of C-terminus.

In some embodiments, conservative mutations can be introduced intoantibody sequences (e.g., CDRs or framework sequences) at positionswhere the residues are not likely to be involved in interacting with atarget antigen (e.g., transferrin receptor), for example, as determinedbased on a crystal structure. In some embodiments, one, two or moremutations (e.g., amino acid substitutions) are introduced into the Fcregion of an anti-TfR antibody described herein (e.g., in a CH2 domain(residues 231-340 of human IgG1) and/or (e.g., and) CH3 domain (residues341-447 of human IgG1) and/or (e.g., and) the hinge region, withnumbering according to the Kabat numbering system (e.g., the EU index inKabat)) to alter one or more functional properties of the antibody, suchas serum half-life, complement fixation, Fc receptor binding and/or(e.g., and) antigen-dependent cellular cytotoxicity.

In some embodiments, one, two or more mutations (e.g., amino acidsubstitutions) are introduced into the hinge region of the Fc region(CH1 domain) such that the number of cysteine residues in the hingeregion are altered (e.g., increased or decreased) as described in, e.g.,U.S. Pat. No. 5,677,425. The number of cysteine residues in the hingeregion of the CH1 domain can be altered to, e.g., facilitate assembly ofthe light and heavy chains, or to alter (e.g., increase or decrease) thestability of the antibody or to facilitate linker conjugation.

In some embodiments, one, two or more mutations (e.g., amino acidsubstitutions) are introduced into the Fc region of a muscle-targetingantibody described herein (e.g., in a CH2 domain (residues 231-340 ofhuman IgG1) and/or (e.g., and) CH3 domain (residues 341-447 of humanIgG1) and/or (e.g., and) the hinge region, with numbering according tothe Kabat numbering system (e.g., the EU index in Kabat)) to increase ordecrease the affinity of the antibody for an Fc receptor (e.g., anactivated Fc receptor) on the surface of an effector cell. Mutations inthe Fc region of an antibody that decrease or increase the affinity ofan antibody for an Fc receptor and techniques for introducing suchmutations into the Fc receptor or fragment thereof are known to one ofskill in the art. Examples of mutations in the Fc receptor of anantibody that can be made to alter the affinity of the antibody for anFc receptor are described in, e.g., Smith P et al., (2012) PNAS 109:6181-6186, U.S. Pat. No. 6,737,056, and International Publication Nos.WO 02/060919; WO 98/23289; and WO 97/34631, which are incorporatedherein by reference.

In some embodiments, one, two or more amino acid mutations (i.e.,substitutions, insertions or deletions) are introduced into an IgGconstant domain, or FcRn-binding fragment thereof (preferably an Fc orhinge-Fc domain fragment) to alter (e.g., decrease or increase)half-life of the antibody in vivo. See, e.g., International PublicationNos. WO 02/060919; WO 98/23289; and WO 97/34631; and U.S. Pat. Nos.5,869,046, 6,121,022, 6,277,375 and 6,165,745 for examples of mutationsthat will alter (e.g., decrease or increase) the half-life of anantibody in vivo.

In some embodiments, one, two or more amino acid mutations (i.e.,substitutions, insertions or deletions) are introduced into an IgGconstant domain, or FcRn-binding fragment thereof (preferably an Fc orhinge-Fc domain fragment) to decrease the half-life of the anti-anti-TfRantibody in vivo. In some embodiments, one, two or more amino acidmutations (i.e., substitutions, insertions or deletions) are introducedinto an IgG constant domain, or FcRn-binding fragment thereof(preferably an Fc or hinge-Fc domain fragment) to increase the half-lifeof the antibody in vivo. In some embodiments, the antibodies can haveone or more amino acid mutations (e.g., substitutions) in the secondconstant (CH2) domain (residues 231-340 of human IgG1) and/or (e.g.,and) the third constant (CH3) domain (residues 341-447 of human IgG1),with numbering according to the EU index in Kabat (Kabat E A et al.,(1991) supra). In some embodiments, the constant region of the IgG1 ofan antibody described herein comprises a methionine (M) to tyrosine (Y)substitution in position 252, a serine (S) to threonine (T) substitutionin position 254, and a threonine (T) to glutamic acid (E) substitutionin position 256, numbered according to the EU index as in Kabat. SeeU.S. Pat. No. 7,658,921, which is incorporated herein by reference. Thistype of mutant IgG, referred to as “YTE mutant” has been shown todisplay fourfold increased half-life as compared to wild-type versionsof the same antibody (see Dall'Acqua W F et al., (2006) J Biol Chem 281:23514-24). In some embodiments, an antibody comprises an IgG constantdomain comprising one, two, three or more amino acid substitutions ofamino acid residues at positions 251-257, 285-290, 308-314, 385-389, and428-436, numbered according to the EU index as in Kabat.

In some embodiments, one, two or more amino acid substitutions areintroduced into an IgG constant domain Fc region to alter the effectorfunction(s) of the anti-anti-TfR antibody. The effector ligand to whichaffinity is altered can be, for example, an Fc receptor or the C1component of complement. This approach is described in further detail inU.S. Pat. Nos. 5,624,821 and 5,648,260. In some embodiments, thedeletion or inactivation (through point mutations or other means) of aconstant region domain can reduce Fc receptor binding of the circulatingantibody thereby increasing tumor localization. See, e.g., U.S. Pat.Nos. 5,585,097 and 8,591,886 for a description of mutations that deleteor inactivate the constant domain and thereby increase tumorlocalization. In some embodiments, one or more amino acid substitutionsmay be introduced into the Fc region of an antibody described herein toremove potential glycosylation sites on Fc region, which may reduce Fcreceptor binding (see, e.g., Shields R L et al., (2001) J Biol Chem 276:6591-604).

In some embodiments, one or more amino in the constant region of ananti-TfR antibody described herein can be replaced with a differentamino acid residue such that the antibody has altered Clq binding and/or(e.g., and) reduced or abolished complement dependent cytotoxicity(CDC). This approach is described in further detail in U.S. Pat. No.6,194,551 (Idusogie et al). In some embodiments, one or more amino acidresidues in the N-terminal region of the CH2 domain of an antibodydescribed herein are altered to thereby alter the ability of theantibody to fix complement. This approach is described further inInternational Publication No. WO 94/29351. In some embodiments, the Fcregion of an antibody described herein is modified to increase theability of the antibody to mediate antibody dependent cellularcytotoxicity (ADCC) and/or (e.g., and) to increase the affinity of theantibody for an Fcγ receptor. This approach is described further inInternational Publication No. WO 00/42072.

In some embodiments, the heavy and/or (e.g., and) light chain variabledomain(s) sequence(s) of the antibodies provided herein can be used togenerate, for example, CDR-grafted, chimeric, humanized, or compositehuman antibodies or antigen-binding fragments, as described elsewhereherein. As understood by one of ordinary skill in the art, any variant,CDR-grafted, chimeric, humanized, or composite antibodies derived fromany of the antibodies provided herein may be useful in the compositionsand methods described herein and will maintain the ability tospecifically bind transferrin receptor, such that the variant,CDR-grafted, chimeric, humanized, or composite antibody has at least50%, at least 60%, at least 70%, at least 80%, at least 90%, at least95% or more binding to transferrin receptor relative to the originalantibody from which it is derived.

In some embodiments, the antibodies provided herein comprise mutationsthat confer desirable properties to the antibodies. For example, toavoid potential complications due to Fab-arm exchange, which is known tooccur with native IgG4 mAbs, the antibodies provided herein may comprisea stabilizing ‘Adair’ mutation (Angal S., et al., “A single amino acidsubstitution abolishes the heterogeneity of chimeric mouse/human (IgG4)antibody,” Mol Immunol 30, 105-108; 1993), where serine 228 (EUnumbering; residue 241 Kabat numbering) is converted to prolineresulting in an IgG1-like hinge sequence. Accordingly, any of theantibodies may include a stabilizing ‘Adair’ mutation.

In some embodiments, an antibody is modified, e.g., modified viaglycosylation, phosphorylation, sumoylation, and/or (e.g., and)methylation. In some embodiments, an antibody is a glycosylatedantibody, which is conjugated to one or more sugar or carbohydratemolecules. In some embodiments, the one or more sugar or carbohydratemolecule are conjugated to the antibody via N-glycosylation,O-glycosylation, C-glycosylation, glypiation (GPI anchor attachment),and/or (e.g., and) phosphoglycosylation. In some embodiments, the one ormore sugar or carbohydrate molecules are monosaccharides, disaccharides,oligosaccharides, or glycans. In some embodiments, the one or more sugaror carbohydrate molecule is a branched oligosaccharide or a branchedglycan. In some embodiments, the one or more sugar or carbohydratemolecule includes a mannose unit, a glucose unit, an N-acetylglucosamineunit, an N-acetylgalactosamine unit, a galactose unit, a fucose unit, ora phospholipid unit. In some embodiments, there are about 1-10, about1-5, about 5-10, about 1-4, about 1-3, or about 2 sugar molecules. Insome embodiments, a glycosylated antibody is fully or partiallyglycosylated. In some embodiments, an antibody is glycosylated bychemical reactions or by enzymatic means. In some embodiments, anantibody is glycosylated in vitro or inside a cell, which may optionallybe deficient in an enzyme in the N- or O-glycosylation pathway, e.g. aglycosyltransferase. In some embodiments, an antibody is functionalizedwith sugar or carbohydrate molecules as described in InternationalPatent Application Publication WO2014065661, published on May 1, 2014,entitled, “Modified antibody, antibody-conjugate and process for thepreparation thereof”.

In some embodiments, any one of the anti-TfR1 antibodies describedherein may comprise a signal peptide in the heavy and/or (e.g., and)light chain sequence (e.g., a N-terminal signal peptide). In someembodiments, the anti-TfR1 antibody described herein comprises any oneof the VH and VL sequences, any one of the IgG heavy chain and lightchain sequences, or any one of the Fab heavy chain and light chainsequences described herein, and further comprises a signal peptide(e.g., a N-terminal signal peptide). In some embodiments, the signalpeptide comprises the amino acid sequence of MGWSCIILFLVATATGVHS (SEQ IDNO: 104).

Other Known Anti-Transferrin Receptor Antibodies

Any other appropriate anti-transferrin receptor antibodies known in theart may be used as the muscle-targeting agent in the complexes disclosedherein. Examples of known anti-transferrin receptor antibodies,including associated references and binding epitopes, are listed inTable 8. In some embodiments, the anti-transferrin receptor antibodycomprises the complementarity determining regions (CDR-H1, CDR-H2,CDR-H3, CDR-L1, CDR-L2, and CDR-L3) of any of the anti-transferrinreceptor antibodies provided herein, e.g., anti-transferrin receptorantibodies listed in Table 8.

TABLE 8 List of anti-transferrin receptor antibody clones, includingassociated references and binding epitope information. Antibody CloneName Reference(s) Epitope/Notes OKT9 U.S. Pat. No. 4,364,934, filed Dec.4, 1979, Apical domain of TfR entitled “MONOCLONAL ANTIBODY (residues305-366 of TO A HUMAN EARLY THYMOCYTE human TfR sequence ANTIGEN ANDMETHODS FOR XM_052730.3, PREPARING SAME” available in GenBank) SchneiderC. et al. “Structural features of the cell surface receptor fortransferrin that is recognized by the monoclonal antibody OKT9.” J BiolChem. 1982, 257: 14, 8516- 8522. (From JCR) WO 2015/098989, filed Dec.24, 2014, Apical domain Clone M11 “Novel anti-Transferrin receptor(residues 230-244 and Clone M23 antibody that passes through blood-326-347 of TfR) and Clone M27 brain barrier” protease-like domain CloneB84 U.S. Pat. No. 9,994,641, filed (residues 461-473) Dec. 24, 2014,“Novel anti-Transferrin receptor antibody that passes throughblood-brain barrier” (From WO 2016/081643, filed May 26, 2016, Apicaldomain and Genentech) entitled “ANTI-TRANSFERRIN non-apical regions 7A4,8A2, RECEPTOR ANTIBODIES AND 15D2, 10D11, METHODS OF USE” 7B10, 15G11,U.S. Pat. No. 9,708,406, filed 16G5, 13C3, May 20, 2014,“Anti-transferrin receptor 16G4, 16F6, antibodies and methods of use”7G7, 4C2, 1B12, and 13D4 (From Lee et al. “Targeting Rat Anti-MouseArmagen) Transferrin Receptor Monoclonal 8D3 Antibodies throughBlood-Brain Barrier in Mouse” 2000, J Pharmacol. Exp. Ther., 292:1048-1052. US Patent App. 2010/077498, filed Sep. 11, 2008, entitled“COMPOSITIONS AND METHODS FOR BLOOD- BRAIN BARRIER DELIVERY IN THEMOUSE” OX26 Haobam, B. et al. 2014. Rab17- mediated recycling endosomescontribute to autophagosome formation in response to Group AStreptococcus invasion. Cellular microbiology. 16: 1806-21. DF1513Ortiz-Zapater E et al. Trafficking of the human transferrin receptor inplant cells: effects of tyrphostin A23 and brefeldin A. Plant J 48:757-70 (2006). 1A1B2, 66IG10, Commercially available anti-transferrinNovus Biologicals MEM-189, JF0956, receptor antibodies. 8100 SouthparkWay, 29806, 1A1B2, A-8 Littleton CO TFRC/1818, 1E6, 80120 66Ig10,TFRC/1059, Q1/71, 23D10, 13E4, TFRC/1149, ER-MP21, YTA74.4, BU54, 2B6,RI7 217 (From US Patent App. 2011/0311544A1, filed Does not competeINSERM) Jun. 15, 2005, entitled “ANTI-CD71 with OKT9 BA120g MONOCLONALANTIBODIES AND USES THEREOF FOR TREATING MALIGNANT TUMOR CELLS” LUCA31U.S. Pat. No. 7,572,895, filed “LUCA31 epitope” Jun. 7, 2004, entitled“TRANSFERRIN RECEPTOR ANTIBODIES” (Salk Institute) Trowbridge, I. S. etal. “Anti-transferrin B3/25 receptor monoclonal antibody and T58/30toxin-antibody conjugates affect growth of human tumour cells.” Nature,1981, volume 294, pages 171-173 R17 217.1.3, Commercially availableanti-transferrin BioXcell 5E9C11, OKT9 receptor antibodies. 10Technology Dr., (BE0023 Suite 2B clone) West Lebanon, NH 03784-1671 USABK19.9, Gatter, K. C. et al. “Transferrin B3/25, T56/14 receptors inhuman tissues: their and T58/1 distribution and possible clinicalrelevance.” J Clin Pathol. 1983 May; 36(5): 539-45.

In some embodiments, transferrin receptor antibodies of the presentdisclosure include one or more of the CDR-H (e.g., CDR-H1, CDR-H2, andCDR-H3) amino acid sequences from any one of the anti-transferrinreceptor antibodies selected from Table 8. In some embodiments,transferrin receptor antibodies include the CDR-H1, CDR-H2, and CDR-H3as provided for any one of the anti-transferrin receptor antibodiesselected from Table 8. In some embodiments, anti-transferrin receptorantibodies include the CDR-L1, CDR-L2, and CDR-L3 as provided for anyone of the anti-transferrin receptor antibodies selected from Table 8.In some embodiments, anti-transferrin antibodies include the CDR-H1,CDR-H2, CDR-H3, CDR-L1, CDR-L2, and CDR-L3 as provided for any one ofthe anti-transferrin receptor antibodies selected from Table 8. Thedisclosure also includes any nucleic acid sequence that encodes amolecule comprising a CDR-H1, CDR-H2, CDR-H3, CDR-L1, CDR-L2, or CDR-L3as provided for any one of the anti-transferrin receptor antibodiesselected from Table 8. In some embodiments, antibody heavy and lightchain CDR3 domains may play a particularly important role in the bindingspecificity/affinity of an antibody for an antigen. Accordingly,anti-transferrin receptor antibodies of the disclosure may include atleast the heavy and/or (e.g., and) light chain CDR3s of any one of theanti-transferrin receptor antibodies selected from Table 8.

In some examples, any of the anti-transferrin receptor antibodies of thedisclosure have one or more CDR (e.g., CDR-H or CDR-L) sequencessubstantially similar to any of the CDR-H1, CDR-H2, CDR-H3, CDR-L1,CDR-L2, and/or (e.g., and) CDR-L3 sequences from one of theanti-transferrin receptor antibodies selected from Table 8. In someembodiments, the position of one or more CDRs along the VH (e.g.,CDR-H1, CDR-H2, or CDR-H3) and/or (e.g., and) VL (e.g., CDR-L1, CDR-L2,or CDR-L3) region of an antibody described herein can vary by one, two,three, four, five, or six amino acid positions so long as immunospecificbinding to transferrin receptor (e.g., human transferrin receptor) ismaintained (e.g., substantially maintained, for example, at least 50%,at least 60%, at least 70%, at least 80%, at least 90%, at least 95% ofthe binding of the original antibody from which it is derived). Forexample, in some embodiments, the position defining a CDR of anyantibody described herein can vary by shifting the N-terminal and/or(e.g., and) C-terminal boundary of the CDR by one, two, three, four,five, or six amino acids, relative to the CDR position of any one of theantibodies described herein, so long as immunospecific binding totransferrin receptor (e.g., human transferrin receptor) is maintained(e.g., substantially maintained, for example, at least 50%, at least60%, at least 70%, at least 80%, at least 90%, at least 95% of thebinding of the original antibody from which it is derived). In anotherembodiment, the length of one or more CDRs along the VH (e.g., CDR-H1,CDR-H2, or CDR-H3) and/or (e.g., and) VL (e.g., CDR-L1, CDR-L2, orCDR-L3) region of an antibody described herein can vary (e.g., beshorter or longer) by one, two, three, four, five, or more amino acids,so long as immunospecific binding to transferrin receptor (e.g., humantransferrin receptor) is maintained (e.g., substantially maintained, forexample, at least 50%, at least 60%, at least 70%, at least 80%, atleast 90%, at least 95% of the binding of the original antibody fromwhich it is derived).

Accordingly, in some embodiments, a CDR-L1, CDR-L2, CDR-L3, CDR-H1,CDR-H2, and/or (e.g., and) CDR-H3 described herein may be one, two,three, four, five or more amino acids shorter than one or more of theCDRs described herein (e.g., CDRS from any of the anti-transferrinreceptor antibodies selected from Table 8) so long as immunospecificbinding to transferrin receptor (e.g., human transferrin receptor) ismaintained (e.g., substantially maintained, for example, at least 50%,at least 60%, at least 70%, at least 80%, at least 90%, at least 95%relative to the binding of the original antibody from which it isderived). In some embodiments, a CDR-L1, CDR-L2, CDR-L3, CDR-H1, CDR-H2,and/or (e.g., and) CDR-H3 described herein may be one, two, three, four,five or more amino acids longer than one or more of the CDRs describedherein (e.g., CDRS from any of the anti-transferrin receptor antibodiesselected from Table 8) so long as immunospecific binding to transferrinreceptor (e.g., human transferrin receptor) is maintained (e.g.,substantially maintained, for example, at least 50%, at least 60%, atleast 70%, at least 80%, at least 90%, at least 95% relative to thebinding of the original antibody from which it is derived). In someembodiments, the amino portion of a CDR-L1, CDR-L2, CDR-L3, CDR-H1,CDR-H2, and/or (e.g., and) CDR-H3 described herein can be extended byone, two, three, four, five or more amino acids compared to one or moreof the CDRs described herein (e.g., CDRS from any of theanti-transferrin receptor antibodies selected from Table 8) so long asimmunospecific binding to transferrin receptor (e.g., human transferrinreceptor is maintained (e.g., substantially maintained, for example, atleast 50%, at least 60%, at least 70%, at least 80%, at least 90%, atleast 95% relative to the binding of the original antibody from which itis derived). In some embodiments, the carboxy portion of a CDR-L1,CDR-L2, CDR-L3, CDR-H1, CDR-H2, and/or (e.g., and) CDR-H3 describedherein can be extended by one, two, three, four, five or more aminoacids compared to one or more of the CDRs described herein (e.g., CDRSfrom any of the anti-transferrin receptor antibodies selected from Table8) so long as immunospecific binding to transferrin receptor (e.g.,human transferrin receptor) is maintained (e.g., substantiallymaintained, for example, at least 50%, at least 60%, at least 70%, atleast 80%, at least 90%, at least 95% relative to the binding of theoriginal antibody from which it is derived). In some embodiments, theamino portion of a CDR-L1, CDR-L2, CDR-L3, CDR-H1, CDR-H2, and/or (e.g.,and) CDR-H3 described herein can be shortened by one, two, three, four,five or more amino acids compared to one or more of the CDRs describedherein (e.g., CDRS from any of the anti-transferrin receptor antibodiesselected from Table 8) so long as immunospecific binding to transferrinreceptor (e.g., human transferrin receptor) is maintained (e.g.,substantially maintained, for example, at least 50%, at least 60%, atleast 70%, at least 80%, at least 90%, at least 95% relative to thebinding of the original antibody from which it is derived). In someembodiments, the carboxy portion of a CDR-L1, CDR-L2, CDR-L3, CDR-H1,CDR-H2, and/or (e.g., and) CDR-H3 described herein can be shortened byone, two, three, four, five or more amino acids compared to one or moreof the CDRs described herein (e.g., CDRS from any of theanti-transferrin receptor antibodies selected from Table 8) so long asimmunospecific binding to transferrin receptor (e.g., human transferrinreceptor) is maintained (e.g., substantially maintained, for example, atleast 50%, at least 60%, at least 70%, at least 80%, at least 90%, atleast 95% relative to the binding of the original antibody from which itis derived). Any method can be used to ascertain whether immunospecificbinding to transferrin receptor (e.g., human transferrin receptor) ismaintained, for example, using binding assays and conditions describedin the art.

In some examples, any of the anti-transferrin receptor antibodies of thedisclosure have one or more CDR (e.g., CDR-H or CDR-L) sequencessubstantially similar to any one of the anti-transferrin receptorantibodies selected from Table 8. For example, the antibodies mayinclude one or more CDR sequence(s) from any of the anti-transferrinreceptor antibodies selected from Table 8 containing up to 5, 4, 3, 2,or 1 amino acid residue variations as compared to the corresponding CDRregion in any one of the CDRs provided herein (e.g., CDRs from any ofthe anti-transferrin receptor antibodies selected from Table 8) so longas immunospecific binding to transferrin receptor (e.g., humantransferrin receptor) is maintained (e.g., substantially maintained, forexample, at least 50%, at least 60%, at least 70%, at least 80%, atleast 90%, at least 95% relative to the binding of the original antibodyfrom which it is derived). In some embodiments, any of the amino acidvariations in any of the CDRs provided herein may be conservativevariations. Conservative variations can be introduced into the CDRs atpositions where the residues are not likely to be involved ininteracting with a transferrin receptor protein (e.g., a humantransferrin receptor protein), for example, as determined based on acrystal structure. Some aspects of the disclosure provide transferrinreceptor antibodies that comprise one or more of the heavy chainvariable (VH) and/or (e.g., and) light chain variable (VL) domainsprovided herein. In some embodiments, any of the VH domains providedherein include one or more of the CDR-H sequences (e.g., CDR-H1, CDR-H2,and CDR-H3) provided herein, for example, any of the CDR-H sequencesprovided in any one of the anti-transferrin receptor antibodies selectedfrom Table 8. In some embodiments, any of the VL domains provided hereininclude one or more of the CDR-L sequences (e.g., CDR-L1, CDR-L2, andCDR-L3) provided herein, for example, any of the CDR-L sequencesprovided in any one of the anti-transferrin receptor antibodies selectedfrom Table 8.

In some embodiments, anti-transferrin receptor antibodies of thedisclosure include any antibody that includes a heavy chain variabledomain and/or (e.g., and) a light chain variable domain of anyanti-transferrin receptor antibody, such as any one of theanti-transferrin receptor antibodies selected from Table 8. In someembodiments, anti-transferrin receptor antibodies of the disclosureinclude any antibody that includes the heavy chain variable and lightchain variable pairs of any anti-transferrin receptor antibody, such asany one of the anti-transferrin receptor antibodies selected from Table8.

Aspects of the disclosure provide anti-transferrin receptor antibodieshaving a heavy chain variable (VH) and/or (e.g., and) a light chainvariable (VL) domain amino acid sequence homologous to any of thosedescribed herein. In some embodiments, the anti-transferrin receptorantibody comprises a heavy chain variable sequence or a light chainvariable sequence that is at least 75% (e.g., 80%, 85%, 90%, 95%, 98%,or 99%) identical to the heavy chain variable sequence and/or any lightchain variable sequence of any anti-transferrin receptor antibody, suchas any one of the anti-transferrin receptor antibodies selected fromTable 8. In some embodiments, the homologous heavy chain variable and/or(e.g., and) a light chain variable amino acid sequences do not varywithin any of the CDR sequences provided herein. For example, in someembodiments, the degree of sequence variation (e.g., 75%, 80%, 85%, 90%,95%, 98%, or 99%) may occur within a heavy chain variable and/or (e.g.,and) a light chain variable sequence excluding any of the CDR sequencesprovided herein. In some embodiments, any of the anti-transferrinreceptor antibodies provided herein comprise a heavy chain variablesequence and a light chain variable sequence that comprises a frameworksequence that is at least 75%, 80%, 85%, 90%, 95%, 98%, or 99% identicalto the framework sequence of any anti-transferrin receptor antibody,such as any one of the anti-transferrin receptor antibodies selectedfrom Table 8.

In some embodiments, an anti-transferrin receptor antibody, whichspecifically binds to transferrin receptor (e.g., human transferrinreceptor), comprises a light chain variable VL domain comprising any ofthe CDR-L domains (CDR-L1, CDR-L2, and CDR-L3), or CDR-L domain variantsprovided herein, of any of the anti-transferrin receptor antibodiesselected from Table 8. In some embodiments, an anti-transferrin receptorantibody, which specifically binds to transferrin receptor (e.g., humantransferrin receptor), comprises a light chain variable VL domaincomprising the CDR-L1, the CDR-L2, and the CDR-L3 of anyanti-transferrin receptor antibody, such as any one of theanti-transferrin receptor antibodies selected from Table 8. In someembodiments, the anti-transferrin receptor antibody comprises a lightchain variable (VL) region sequence comprising one, two, three or fourof the framework regions of the light chain variable region sequence ofany anti-transferrin receptor antibody, such as any one of theanti-transferrin receptor antibodies selected from Table 8. In someembodiments, the anti-transferrin receptor antibody comprises one, two,three or four of the framework regions of a light chain variable regionsequence which is at least 75%, 80%, 85%, 90%, 95%, or 100% identical toone, two, three or four of the framework regions of the light chainvariable region sequence of any anti-transferrin receptor antibody, suchas any one of the anti-transferrin receptor antibodies selected fromTable 8. In some embodiments, the light chain variable framework regionthat is derived from said amino acid sequence consists of said aminoacid sequence but for the presence of up to 10 amino acid substitutions,deletions, and/or (e.g., and) insertions, preferably up to 10 amino acidsubstitutions. In some embodiments, the light chain variable frameworkregion that is derived from said amino acid sequence consists of saidamino acid sequence with 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 amino acidresidues being substituted for an amino acid found in an analogousposition in a corresponding non-human, primate, or human light chainvariable framework region.

In some embodiments, an anti-transferrin receptor antibody thatspecifically binds to transferrin receptor comprises the CDR-L1, theCDR-L2, and the CDR-L3 of any anti-transferrin receptor antibody, suchas any one of the anti-transferrin receptor antibodies selected fromTable 8. In some embodiments, the antibody further comprises one, two,three or all four VL framework regions derived from the VL of a human orprimate antibody. The primate or human light chain framework region ofthe antibody selected for use with the light chain CDR sequencesdescribed herein, can have, for example, at least 70% (e.g., at least75%, 80%, 85%, 90%, 95%, 98%, or at least 99%) identity with a lightchain framework region of a non-human parent antibody. The primate orhuman antibody selected can have the same or substantially the samenumber of amino acids in its light chain complementarity determiningregions to that of the light chain complementarity determining regionsof any of the antibodies provided herein, e.g., any of theanti-transferrin receptor antibodies selected from Table 8. In someembodiments, the primate or human light chain framework region aminoacid residues are from a natural primate or human antibody light chainframework region having at least 75% identity, at least 80% identity, atleast 85% identity, at least 90% identity, at least 95% identity, atleast 98% identity, at least 99% (or more) identity with the light chainframework regions of any anti-transferrin receptor antibody, such as anyone of the anti-transferrin receptor antibodies selected from Table 8.In some embodiments, an anti-transferrin receptor antibody furthercomprises one, two, three or all four VL framework regions derived froma human light chain variable kappa subfamily. In some embodiments, ananti-transferrin receptor antibody further comprises one, two, three orall four VL framework regions derived from a human light chain variablelambda subfamily.

In some embodiments, any of the anti-transferrin receptor antibodiesprovided herein comprise a light chain variable domain that furthercomprises a light chain constant region. In some embodiments, the lightchain constant region is a kappa, or a lambda light chain constantregion. In some embodiments, the kappa or lambda light chain constantregion is from a mammal, e.g., from a human, monkey, rat, or mouse. Insome embodiments, the light chain constant region is a human kappa lightchain constant region. In some embodiments, the light chain constantregion is a human lambda light chain constant region. It should beappreciated that any of the light chain constant regions provided hereinmay be variants of any of the light chain constant regions providedherein. In some embodiments, the light chain constant region comprisesan amino acid sequence that is at least 75%, 80%, 85%, 90%, 95%, 98%, or99% identical to any of the light chain constant regions of anyanti-transferrin receptor antibody, such as any one of theanti-transferrin receptor antibodies selected from Table 8.

In some embodiments, the anti-transferrin receptor antibody is anyanti-transferrin receptor antibody, such as any one of theanti-transferrin receptor antibodies selected from Table 8.

In some embodiments, an anti-transferrin receptor antibody comprises aVL domain comprising the amino acid sequence of any anti-transferrinreceptor antibody, such as any one of the anti-transferrin receptorantibodies selected from Table 8, and wherein the constant regionscomprise the amino acid sequences of the constant regions of an IgG,IgE, IgM, IgD, IgA or IgY immunoglobulin molecule, or a human IgG, IgE,IgM, IgD, IgA or IgY immunoglobulin molecule. In some embodiments, ananti-transferrin receptor antibody comprises any of the VL domains, orVL domain variants, and any of the VH domains, or VH domain variants,wherein the VL and VH domains, or variants thereof, are from the sameantibody clone, and wherein the constant regions comprise the amino acidsequences of the constant regions of an IgG, IgE, IgM, IgD, IgA or IgYimmunoglobulin molecule, any class (e.g., IgG1, IgG2, IgG3, IgG4, IgA1and IgA2), or any subclass (e.g., IgG2a and IgG2b) of immunoglobulinmolecule. Non-limiting examples of human constant regions are describedin the art, e.g., see Kabat E A et al., (1991) supra.

In some embodiments, the muscle-targeting agent is a transferrinreceptor antibody (e.g., the antibody and variants thereof as describedin International Application Publication WO 2016/081643, incorporatedherein by reference).

The heavy chain and light chain CDRs of the antibody according todifferent definition systems are provided in Table 9. The differentdefinition systems, e.g., the Kabat definition, the Chothia definition,and/or (e.g., and) the contact definition have been described. See,e.g., (e.g., Kabat, E. A., et al. (1991) Sequences of Proteins ofImmunological Interest, Fifth Edition, U.S. Department of Health andHuman Services, NIH Publication No. 91-3242, Chothia et al., (1989)Nature 342:877; Chothia, C. et al. (1987) J. Mol. Biol. 196:901-917,Al-lazikani et al (1997) J. Molec. Biol. 273:927-948; and Almagro, J.Mol. Recognit. 17:132-143 (2004). See also hgmp.mrc.ac.uk andbioinf.org.uk/abs).

TABLE 9 Heavy chain and light chain CDRs of amouse transferrin receptor antibody CDRs Kabat Chothia Contact CDR-H1SYWMH (SEQ GYTFTSY (SEQ TSYWMH (SEQ ID NO: 110) ID NO: 116) ID NO: 118)CDR-H2 EINPTNGRTNY NPTNGR (SEQ WIGEINPTNGR IEKFKS (SEQ ID NO: 117)TN (SEQ ID ID NO: 111) NO: 119) CDR-H3 GTRAYHY GTRAYHY (SEQ ARGTRA (SEQ(SEQ ID NO: ID NO: 112) ID NO: 120) 112) CDR-L1 RASDNLYSNLA RASDNLYSNLAYSNLAWY (SEQ ID NO: (SEQ ID NO: (SEQ ID NO: 113) 113) 121) CDR-L2DATNLAD DATNLAD (SEQ LLVYDATNLA (SEQ ID NO: ID NO: 114) (SEQ ID NO: 114)122) CDR-L3 QHFWGTPLT QHFWGTPLT QHFWGTPL (SEQ ID NO: (SEQ ID NO:(SEQ ID NO: 115) 115) 123)

The heavy chain variable domain (VH) and light chain variable domainsequences are also provided:

VH (SEQ ID NO: 124) QVQLQQPGAELVKPGASVKLSCKASGYTFTSYWMHWVKQRPGQGLEWIGEINPTNGRTNYIEKFKSKATLTVDKSSSTAYMQLSSLTSEDSAVYYCARGT RAYHYWGQGTSVTVSS VL(SEQ ID NO: 125) DIQMTQSPASLSVSVGETVTITCRASDNLYSNLAWYQQKQGKSPQLLVYDATNLADGVPSRFSGSGSGTQYSLKINSLQSEDFGTYYCQHFWGTPLTFGA GTKLELK

In some embodiments, the transferrin receptor antibody of the presentdisclosure comprises a CDR-H1, a CDR-H2, and a CDR-H3 that are the sameas the CDR-H1, CDR-H2, and CDR-H3 shown in Table 9. Alternatively or inaddition (e.g., in addition), the transferrin receptor antibody of thepresent disclosure comprises a CDR-L1, a CDR-L2, and a CDR-L3 that arethe same as the CDR-L1, CDR-L2, and CDR-L3 shown in Table 9.

In some embodiments, the transferrin receptor antibody of the presentdisclosure comprises a CDR-H1, a CDR-H2, and a CDR-H3, whichcollectively contains no more than 5 amino acid variations (e.g., nomore than 5, 4, 3, 2, or 1 amino acid variation) as compared with theCDR-H1, CDR-H2, and CDR-H3 as shown in Table 9. “Collectively” meansthat the total number of amino acid variations in all of the three heavychain CDRs is within the defined range. Alternatively or in addition(e.g., in addition), the transferrin receptor antibody of the presentdisclosure may comprise a CDR-L1, a CDR-L2, and a CDR-L3, whichcollectively contains no more than 5 amino acid variations (e.g., nomore than 5, 4, 3, 2 or 1 amino acid variation) as compared with theCDR-L1, CDR-L2, and CDR-L3 as shown in Table 9.

In some embodiments, the transferrin receptor antibody of the presentdisclosure comprises a CDR-H1, a CDR-H2, and a CDR-H3, at least one ofwhich contains no more than 3 amino acid variations (e.g., no more than3, 2, or 1 amino acid variation) as compared with the counterpart heavychain CDR as shown in Table 9. Alternatively or in addition (e.g., inaddition), the transferrin receptor antibody of the present disclosuremay comprise CDR-L1, a CDR-L2, and a CDR-L3, at least one of whichcontains no more than 3 amino acid variations (e.g., no more than 3, 2,or 1 amino acid variation) as compared with the counterpart light chainCDR as shown in Table 9.

In some embodiments, the transferrin receptor antibody of the presentdisclosure comprises a CDR-L3, which contains no more than 3 amino acidvariations (e.g., no more than 3, 2, or 1 amino acid variation) ascompared with the CDR-L3 as shown in Table 9. In some embodiments, thetransferrin receptor antibody of the present disclosure comprises aCDR-L3 containing one amino acid variation as compared with the CDR-L3as shown in Table 9. In some embodiments, the transferrin receptorantibody of the present disclosure comprises a CDR-L3 of QHFAGTPLT (SEQID NO: 126) according to the Kabat and Chothia definition system) orQHFAGTPL (SEQ ID NO: 127) according to the Contact definition system).In some embodiments, the transferrin receptor antibody of the presentdisclosure comprises a CDR-H1, a CDR-H2, a CDR-H3, a CDR-L1 and a CDR-L2that are the same as the CDR-H1, CDR-H2, and CDR-H3 shown in Table 9,and comprises a CDR-L3 of QHFAGTPLT (SEQ ID NO: 126) according to theKabat and Chothia definition system) or QHFAGTPL (SEQ ID NO: 127)according to the Contact definition system).

In some embodiments, the transferrin receptor antibody of the presentdisclosure comprises heavy chain CDRs that collectively are at least 80%(e.g., 80%, 85%, 90%, 95%, or 98%) identical to the heavy chain CDRs asshown in Table 9. Alternatively or in addition (e.g., in addition), thetransferrin receptor antibody of the present disclosure comprises lightchain CDRs that collectively are at least 80% (e.g., 80%, 85%, 90%, 95%,or 98%) identical to the light chain CDRs as shown in Table 9.

In some embodiments, the transferrin receptor antibody of the presentdisclosure comprises a VH comprising the amino acid sequence of SEQ IDNO: 124. Alternatively or in addition (e.g., in addition), thetransferrin receptor antibody of the present disclosure comprises a VLcomprising the amino acid sequence of SEQ ID NO: 125.

In some embodiments, the transferrin receptor antibody of the presentdisclosure comprises a VH containing no more than 25 amino acidvariations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16,15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acidvariation) as compared with the VH as set forth in SEQ ID NO: 124.Alternatively or in addition (e.g., in addition), the transferrinreceptor antibody of the present disclosure comprises a VL containing nomore than 15 amino acid variations (e.g., no more than 20, 19, 18, 17,16, 15, 14, 13, 12, 11, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acidvariation) as compared with the VL as set forth in SEQ ID NO: 125.

In some embodiments, the transferrin receptor antibody of the presentdisclosure comprises a VH comprising an amino acid sequence that is atleast 80% (e.g., 80%, 85%, 90%, 95%, or 98%) identical to the VH as setforth in SEQ ID NO: 124. Alternatively or in addition (e.g., inaddition), the transferrin receptor antibody of the present disclosurecomprises a VL comprising an amino acid sequence that is at least 80%(e.g., 80%, 85%, 90%, 95%, or 98%) identical to the VL as set forth inSEQ ID NO: 125.

In some embodiments, the transferrin receptor antibody of the presentdisclosure is a humanized antibody (e.g., a humanized variant of anantibody). In some embodiments, the transferrin receptor antibody of thepresent disclosure comprises a CDR-H1, a CDR-H2, a CDR-H3, a CDR-L1, aCDR-L2, and a CDR-L3 that are the same as the CDR-H1, CDR-H2, and CDR-H3shown in Table 9, and comprises a humanized heavy chain variable regionand/or (e.g., and) a humanized light chain variable region.

Humanized antibodies are human immunoglobulins (recipient antibody) inwhich residues from a complementary determining region (CDR) of therecipient are replaced by residues from a CDR of a non-human species(donor antibody) such as mouse, rat, or rabbit having the desiredspecificity, affinity, and capacity. In some embodiments, Fv frameworkregion (FR) residues of the human immunoglobulin are replaced bycorresponding non-human residues. Furthermore, the humanized antibodymay comprise residues that are found neither in the recipient antibodynor in the imported CDR or framework sequences, but are included tofurther refine and optimize antibody performance. In general, thehumanized antibody will comprise substantially all of at least one, andtypically two, variable domains, in which all or substantially all ofthe CDR regions correspond to those of a non-human immunoglobulin andall or substantially all of the FR regions are those of a humanimmunoglobulin consensus sequence. The humanized antibody optimally alsowill comprise at least a portion of an immunoglobulin constant region ordomain (Fc), typically that of a human immunoglobulin. Antibodies mayhave Fc regions modified as described in WO 99/58572. Other forms ofhumanized antibodies have one or more CDRs (one, two, three, four, five,six) which are altered with respect to the original antibody, which arealso termed one or more CDRs derived from one or more CDRs from theoriginal antibody. Humanized antibodies may also involve affinitymaturation.

In some embodiments, humanization is achieved by grafting the CDRs(e.g., as shown in Table 9) into the IGKV1-NL1*01 and IGHV1-3*01 humanvariable domains. In some embodiments, the transferrin receptor antibodyof the present disclosure is a humanized variant comprising one or moreamino acid substitutions at positions 9, 13, 17, 18, 40, 45, and 70 ascompared with the VL as set forth in SEQ ID NO: 125, and/or (e.g., and)one or more amino acid substitutions at positions 1, 5, 7, 11, 12, 20,38, 40, 44, 66, 75, 81, 83, 87, and 108 as compared with the VH as setforth in SEQ ID NO: 124. In some embodiments, the transferrin receptorantibody of the present disclosure is a humanized variant comprisingamino acid substitutions at all of positions 9, 13, 17, 18, 40, 45, and70 as compared with the VL as set forth in SEQ ID NO: 125, and/or (e.g.,and) amino acid substitutions at all of positions 1, 5, 7, 11, 12, 20,38, 40, 44, 66, 75, 81, 83, 87, and 108 as compared with the VH as setforth in SEQ ID NO: 124.

In some embodiments, the transferrin receptor antibody of the presentdisclosure is a humanized antibody and contains the residues atpositions 43 and 48 of the VL as set forth in SEQ ID NO: 125.Alternatively or in addition (e.g., in addition), the transferrinreceptor antibody of the present disclosure is a humanized antibody andcontains the residues at positions 48, 67, 69, 71, and 73 of the VH asset forth in SEQ ID NO: 124.

The VH and VL amino acid sequences of an example humanized antibody thatmay be used in accordance with the present disclosure are provided:

Humanized VH (SEQ ID NO: 128)EVQLVQSGAEVKKPGASVKVSCKASGYTFTSYWMHWVRQAPGQRLEWIGEINPTNGRTNYIEKFKSRATLTVDKSASTAYMELSSLRSEDTAVYYCARGT RAYHYWGQGTMVTVSSHumanized VL (SEQ ID NO: 129)DIQMTQSPSSLSASVGDRVTITCRASDNLYSNLAWYQQKPGKSPKLLVYDATNLADGVPSRFSGSGSGTDYTLTISSLQPEDFATYYCQHFWGTPLTFGQ GTKVEIK

In some embodiments, the transferrin receptor antibody of the presentdisclosure comprises a VH comprising the amino acid sequence of SEQ IDNO: 128. Alternatively or in addition (e.g., in addition), thetransferrin receptor antibody of the present disclosure comprises a VLcomprising the amino acid sequence of SEQ ID NO: 129.

In some embodiments, the transferrin receptor antibody of the presentdisclosure comprises a VH containing no more than 25 amino acidvariations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16,15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acidvariation) as compared with the VH as set forth in SEQ ID NO: 128.Alternatively or in addition (e.g., in addition), the transferrinreceptor antibody of the present disclosure comprises a VL containing nomore than 15 amino acid variations (e.g., no more than 20, 19, 18, 17,16, 15, 14, 13, 12, 11, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acidvariation) as compared with the VL as set forth in SEQ ID NO: 129.

In some embodiments, the transferrin receptor antibody of the presentdisclosure comprises a VH comprising an amino acid sequence that is atleast 80% (e.g., 80%, 85%, 90%, 95%, or 98%) identical to the VH as setforth in SEQ ID NO: 128. Alternatively or in addition (e.g., inaddition), the transferrin receptor antibody of the present disclosurecomprises a VL comprising an amino acid sequence that is at least 80%(e.g., 80%, 85%, 90%, 95%, or 98%) identical to the VL as set forth inSEQ ID NO: 129.

In some embodiments, the transferrin receptor antibody of the presentdisclosure is a humanized variant comprising amino acid substitutions atone or more of positions 43 and 48 as compared with the VL as set forthin SEQ ID NO: 125, and/or (e.g., and) amino acid substitutions at one ormore of positions 48, 67, 69, 71, and 73 as compared with the VH as setforth in SEQ ID NO: 124. In some embodiments, the transferrin receptorantibody of the present disclosure is a humanized variant comprising aS43A and/or (e.g., and) a V48L mutation as compared with the VL as setforth in SEQ ID NO: 125, and/or (e.g., and) one or more of A67V, L69I,V71R, and K73T mutations as compared with the VH as set forth in SEQ IDNO: 124.

In some embodiments, the transferrin receptor antibody of the presentdisclosure is a humanized variant comprising amino acid substitutions atone or more of positions 9, 13, 17, 18, 40, 43, 48, 45, and 70 ascompared with the VL as set forth in SEQ ID NO: 125, and/or (e.g., and)amino acid substitutions at one or more of positions 1, 5, 7, 11, 12,20, 38, 40, 44, 48, 66, 67, 69, 71, 73, 75, 81, 83, 87, and 108 ascompared with the VH as set forth in SEQ ID NO: 124.

In some embodiments, the transferrin receptor antibody of the presentdisclosure is a chimeric antibody, which can include a heavy constantregion and a light constant region from a human antibody. Chimericantibodies refer to antibodies having a variable region or part ofvariable region from a first species and a constant region from a secondspecies. Typically, in these chimeric antibodies, the variable region ofboth light and heavy chains mimics the variable regions of antibodiesderived from one species of mammals (e.g., a non-human mammal such asmouse, rabbit, and rat), while the constant portions are homologous tothe sequences in antibodies derived from another mammal such as human.In some embodiments, amino acid modifications can be made in thevariable region and/or (e.g., and) the constant region.

In some embodiments, the transferrin receptor antibody described hereinis a chimeric antibody, which can include a heavy constant region and alight constant region from a human antibody. Chimeric antibodies referto antibodies having a variable region or part of variable region from afirst species and a constant region from a second species. Typically, inthese chimeric antibodies, the variable region of both light and heavychains mimics the variable regions of antibodies derived from onespecies of mammals (e.g., a non-human mammal such as mouse, rabbit, andrat), while the constant portions are homologous to the sequences inantibodies derived from another mammal such as human. In someembodiments, amino acid modifications can be made in the variable regionand/or (e.g., and) the constant region.

In some embodiments, the heavy chain of any of the transferrin receptorantibodies as described herein may comprises a heavy chain constantregion (CH) or a portion thereof (e.g., CH1, CH2, CH3, or a combinationthereof). The heavy chain constant region can of any suitable origin,e.g., human, mouse, rat, or rabbit. In one specific example, the heavychain constant region is from a human IgG (a gamma heavy chain), e.g.,IgG1, IgG2, or IgG4. An example of a human IgG1 constant region is givenbelow:

(SEQ ID NO: 130) ASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK

In some embodiments, the light chain of any of the transferrin receptorantibodies described herein may further comprise a light chain constantregion (CL), which can be any CL known in the art. In some examples, theCL is a kappa light chain. In other examples, the CL is a lambda lightchain. In some embodiments, the CL is a kappa light chain, the sequenceof which is provided below:

(SEQ ID NO: 83) RTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGLSSPVTK SFNRGEC

Other antibody heavy and light chain constant regions are well known inthe art, e.g., those provided in the IMGT database (www.imgt.org) or atwww.vbase2.org/vbstat.php., both of which are incorporated by referenceherein.

Examples of heavy chain and light chain amino acid sequences of thetransferrin receptor antibodies described are provided below:

Heavy Chain (VH + human IgG1 constant region) (SEQ ID NO: 132)QVQLQQPGAELVKPGASVKLSCKASGYTFTSYWMHWVKQRPGQGLEWIGEINPTNGRTNYIEKFKSKATLTVDKSSSTAYMQLSSLTSEDSAVYYCARGTRAYHYWGQGTSVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGKLight Chain (VL + kappa light chain) (SEQ ID NO: 133)DIQMTQSPASLSVSVGETVTITCRASDNLYSNLAWYQQKQGKSPQLLVYDATNLADGVPSRFSGSGSGTQYSLKINSLQSEDFGTYYCQHFWGTPLTFGAGTKLELKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQG LSSPVTKSFNRGECHeavy Chain (humanized VH + human IgG1 constant region) (SEQ ID NO: 134)EVQLVQSGAEVKKPGASVKVSCKASGYTFTSYWMHWVRQAPGQRLEWIGEINPTNGRTNYIEKFKSRATLTVDKSASTAYMELSSLRSEDTAVYYCARGTRAYHYWGQGTMVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDTLMISRTPEVTCVVVDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGKLight Chain (humanized VL + kappa light chain) (SEQ ID NO: 135)DIQMTQSPSSLSASVGDRVTITCRASDNLYSNLAWYQQKPGKSPKLLVYDATNLADGVPSRFSGSGSGTDYTLTISSLQPEDFATYYCQHFWGTPLTFGQGTKVEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQG LSSPVTKSFNRGEC

In some embodiments, the transferrin receptor antibody described hereincomprises a heavy chain comprising an amino acid sequence that is atleast 80% (e.g., 80%, 85%, 90%, 95%, or 98%) identical to SEQ ID NO:132. Alternatively or in addition (e.g., in addition), the transferrinreceptor antibody described herein comprises a light chain comprising anamino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, or98%) identical to SEQ ID NO: 133. In some embodiments, the transferrinreceptor antibody described herein comprises a heavy chain comprisingthe amino acid sequence of SEQ ID NO: 132. Alternatively or in addition(e.g., in addition), the transferrin receptor antibody described hereincomprises a light chain comprising the amino acid sequence of SEQ ID NO:133.

In some embodiments, the transferrin receptor antibody of the presentdisclosure comprises a heavy chain containing no more than 25 amino acidvariations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16,15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acidvariation) as compared with the heavy chain as set forth in SEQ ID NO:132. Alternatively or in addition (e.g., in addition), the transferrinreceptor antibody of the present disclosure comprises a light chaincontaining no more than 15 amino acid variations (e.g., no more than 20,19, 18, 17, 16, 15, 14, 13, 12, 11, 9, 8, 7, 6, 5, 4, 3, 2, or 1 aminoacid variation) as compared with the light chain as set forth in SEQ IDNO: 133.

In some embodiments, the transferrin receptor antibody described hereincomprises a heavy chain comprising an amino acid sequence that is atleast 80% (e.g., 80%, 85%, 90%, 95%, or 98%) identical to SEQ ID NO:134. Alternatively or in addition (e.g., in addition), the transferrinreceptor antibody described herein comprises a light chain comprising anamino acid sequence that is at least 80% (e.g., 80%, 85%, 90%, 95%, or98%) identical to SEQ ID NO: 135. In some embodiments, the transferrinreceptor antibody described herein comprises a heavy chain comprisingthe amino acid sequence of SEQ ID NO: 134. Alternatively or in addition(e.g., in addition), the transferrin receptor antibody described hereincomprises a light chain comprising the amino acid sequence of SEQ ID NO:135.

In some embodiments, the transferrin receptor antibody of the presentdisclosure comprises a heavy chain containing no more than 25 amino acidvariations (e.g., no more than 25, 24, 23, 22, 21, 20, 19, 18, 17, 16,15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 amino acidvariation) as compared with the heavy chain of humanized antibody as setforth in SEQ ID NO: 134. Alternatively or in addition (e.g., inaddition), the transferrin receptor antibody of the present disclosurecomprises a light chain containing no more than 15 amino acid variations(e.g., no more than 20, 19, 18, 17, 16, 15, 14, 13, 12, 11, 9, 8, 7, 6,5, 4, 3, 2, or 1 amino acid variation) as compared with the light chainof humanized antibody as set forth in SEQ ID NO: 135.

In some embodiments, the transferrin receptor antibody is an antigenbinding fragment (FAB) of an intact antibody (full-length antibody).Antigen binding fragment of an intact antibody (full-length antibody)can be prepared via routine methods. For example, F(ab′)2 fragments canbe produced by pepsin digestion of an antibody molecule, and Fab′fragments that can be generated by reducing the disulfide bridges ofF(ab′)2 fragments. Examples of Fab amino acid sequences of thetransferrin receptor antibodies described herein are provided below:

Heavy Chain Fab (VH + a portion of human IgG1 constant region)(SEQ ID NO: 136) QVQLQQPGAELVKPGASVKLSCKASGYTFTSYWMHWVKQRPGQGLEWIGEINPTNGRTNYIEKFKSKATLTVDKSSSTAYMQLSSLTSEDSAVYYCARGTRAYHYWGQGTSVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCP Heavy Chain Fab (humanized VH + a portionof human IgG1 constant region) (SEQ ID NO: 137)EVQLVQSGAEVKKPGASVKVSCKASGYTFTSYWMHWVRQAPGQRLEWIGEINPTNGRTNYIEKFKSRATLTVDKSASTAYMELSSLRSEDTAVYYCARGTRAYHYWGQGTMVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLGTQTYICNVNHKPSNTKVDKKVEPKSCDKTHTCP

In some embodiments, the transferrin receptor antibody described hereincomprises a heavy chain comprising the amino acid sequence of SEQ ID NO:136. Alternatively or in addition (e.g., in addition), the transferrinreceptor antibody described herein comprises a light chain comprisingthe amino acid sequence of SEQ ID NO: 133.

In some embodiments, the transferrin receptor antibody described hereincomprises a heavy chain comprising the amino acid sequence of SEQ ID NO:137. Alternatively or in addition (e.g., in addition), the transferrinreceptor antibody described herein comprises a light chain comprisingthe amino acid sequence of SEQ ID NO: 135.

The transferrin receptor antibodies described herein can be in anyantibody form, including, but not limited to, intact (i.e., full-length)antibodies, antigen-binding fragments thereof (such as Fab, Fab′,F(ab′)2, Fv), single chain antibodies, bi-specific antibodies, ornanobodies. In some embodiments, the transferrin receptor antibodydescribed herein is a scFv.

In some embodiments, the transferrin receptor antibody described hereinis a scFv-Fab (e.g., scFv fused to a portion of a constant region). Insome embodiments, the transferrin receptor antibody described herein isa scFv fused to a constant region (e.g., human IgG1 constant region asset forth in SEQ ID NO: 130).

In some embodiments, any one of the anti-TfR antibodies described hereinis produced by recombinant DNA technology in Chinese hamster ovary (CHO)cell suspension culture, optionally in CHO-K1 cell (e.g., CHO-K1 cellsderived from European Collection of Animal Cell Culture, Cat. No.85051005) suspension culture.

In some embodiments, an antibody provided herein may have one or morepost-translational modifications. In some embodiments, N-terminalcyclization, also called pyroglutamate formation (pyro-Glu), may occurin the antibody at N-terminal Glutamate (Glu) and/or Glutamine (Gln)residues during production. As such, it should be appreciated that anantibody specified as having a sequence comprising an N-terminalglutamate or glutamine residue encompasses antibodies that haveundergone pyroglutamate formation resulting from a post-translationalmodification. In some embodiments, pyroglutamate formation occurs in aheavy chain sequence. In some embodiments, pyroglutamate formationoccurs in a light chain sequence.

b. Other Muscle-Targeting Antibodies

In some embodiments, the muscle-targeting antibody is an antibody thatspecifically binds hemojuvelin, caveolin-3, Duchenne muscular dystrophypeptide, myosin IIb, or CD63. In some embodiments, the muscle-targetingantibody is an antibody that specifically binds a myogenic precursorprotein. Exemplary myogenic precursor proteins include, withoutlimitation, ABCG2, M-Cadherin/Cadherin-15, Caveolin-1, CD34, FoxK1,Integrin alpha 7, Integrin alpha 7 beta 1, MYF-5, MyoD, Myogenin,NCAM-1/CD56, Pax3, Pax7, and Pax9. In some embodiments, themuscle-targeting antibody is an antibody that specifically binds askeletal muscle protein. Exemplary skeletal muscle proteins include,without limitation, alpha-Sarcoglycan, beta-Sarcoglycan, CalpainInhibitors, Creatine Kinase MM/CKMM, eIF5A, Enolase 2/Neuron-specificEnolase, epsilon-Sarcoglycan, FABP3/H-FABP, GDF-8/Myostatin,GDF-11/GDF-8, Integrin alpha 7, Integrin alpha 7 beta 1, Integrin beta1/CD29, MCAM/CD146, MyoD, Myogenin, Myosin Light Chain KinaseInhibitors, NCAM-1/CD56, and Troponin I. In some embodiments, themuscle-targeting antibody is an antibody that specifically binds asmooth muscle protein. Exemplary smooth muscle proteins include, withoutlimitation, alpha-Smooth Muscle Actin, VE-Cadherin, Caldesmon/CALD1,Calponin 1, Desmin, Histamine H2 R, Motilin R/GPR38, Transgelin/TAGLN,and Vimentin. However, it should be appreciated that antibodies toadditional targets are within the scope of this disclosure and theexemplary lists of targets provided herein are not meant to be limiting.

c. Antibody Features/Alterations

In some embodiments, conservative mutations can be introduced intoantibody sequences (e.g., CDRs or framework sequences) at positionswhere the residues are not likely to be involved in interacting with atarget antigen (e.g., transferrin receptor), for example, as determinedbased on a crystal structure. In some embodiments, one, two or moremutations (e.g., amino acid substitutions) are introduced into the Fcregion of a muscle-targeting antibody described herein (e.g., in a CH2domain (residues 231-340 of human IgG1) and/or (e.g., and) CH3 domain(residues 341-447 of human IgG1) and/or (e.g., and) the hinge region,with numbering according to the Kabat numbering system (e.g., the EUindex in Kabat)) to alter one or more functional properties of theantibody, such as serum half-life, complement fixation, Fc receptorbinding and/or (e.g., and) antigen-dependent cellular cytotoxicity.

In some embodiments, one, two or more mutations (e.g., amino acidsubstitutions) are introduced into the hinge region of the Fc region(CH1 domain) such that the number of cysteine residues in the hingeregion are altered (e.g., increased or decreased) as described in, e.g.,U.S. Pat. No. 5,677,425. The number of cysteine residues in the hingeregion of the CH1 domain can be altered to, e.g., facilitate assembly ofthe light and heavy chains, or to alter (e.g., increase or decrease) thestability of the antibody or to facilitate linker conjugation.

In some embodiments, one, two or more mutations (e.g., amino acidsubstitutions) are introduced into the Fc region of a muscle-targetingantibody described herein (e.g., in a CH2 domain (residues 231-340 ofhuman IgG1) and/or (e.g., and) CH3 domain (residues 341-447 of humanIgG1) and/or (e.g., and) the hinge region, with numbering according tothe Kabat numbering system (e.g., the EU index in Kabat)) to increase ordecrease the affinity of the antibody for an Fc receptor (e.g., anactivated Fc receptor) on the surface of an effector cell. Mutations inthe Fc region of an antibody that decrease or increase the affinity ofan antibody for an Fc receptor and techniques for introducing suchmutations into the Fc receptor or fragment thereof are known to one ofskill in the art. Examples of mutations in the Fc receptor of anantibody that can be made to alter the affinity of the antibody for anFc receptor are described in, e.g., Smith P et al., (2012) PNAS 109:6181-6186, U.S. Pat. No. 6,737,056, and International Publication Nos.WO 02/060919; WO 98/23289; and WO 97/34631, which are incorporatedherein by reference.

In some embodiments, one, two or more amino acid mutations (i.e.,substitutions, insertions or deletions) are introduced into an IgGconstant domain, or FcRn-binding fragment thereof (preferably an Fc orhinge-Fc domain fragment) to alter (e.g., decrease or increase)half-life of the antibody in vivo. See, e.g., International PublicationNos. WO 02/060919; WO 98/23289; and WO 97/34631; and U.S. Pat. Nos.5,869,046, 6,121,022, 6,277,375 and 6,165,745 for examples of mutationsthat will alter (e.g., decrease or increase) the half-life of anantibody in vivo.

In some embodiments, one, two or more amino acid mutations (i.e.,substitutions, insertions or deletions) are introduced into an IgGconstant domain, or FcRn-binding fragment thereof (preferably an Fc orhinge-Fc domain fragment) to decrease the half-life of theanti-transferrin receptor antibody in vivo. In some embodiments, one,two or more amino acid mutations (i.e., substitutions, insertions ordeletions) are introduced into an IgG constant domain, or FcRn-bindingfragment thereof (preferably an Fc or hinge-Fc domain fragment) toincrease the half-life of the antibody in vivo. In some embodiments, theantibodies can have one or more amino acid mutations (e.g.,substitutions) in the second constant (CH2) domain (residues 231-340 ofhuman IgG1) and/or (e.g., and) the third constant (CH3) domain (residues341-447 of human IgG1), with numbering according to the EU index inKabat (Kabat E A et al., (1991) supra). In some embodiments, theconstant region of the IgG1 of an antibody described herein comprises amethionine (M) to tyrosine (Y) substitution in position 252, a serine(S) to threonine (T) substitution in position 254, and a threonine (T)to glutamic acid (E) substitution in position 256, numbered according tothe EU index as in Kabat. See U.S. Pat. No. 7,658,921, which isincorporated herein by reference. This type of mutant IgG, referred toas “YTE mutant” has been shown to display fourfold increased half-lifeas compared to wild-type versions of the same antibody (see Dall'Acqua WF et al., (2006) J Biol Chem 281: 23514-24). In some embodiments, anantibody comprises an IgG constant domain comprising one, two, three ormore amino acid substitutions of amino acid residues at positions251-257, 285-290, 308-314, 385-389, and 428-436, numbered according tothe EU index as in Kabat.

In some embodiments, one, two or more amino acid substitutions areintroduced into an IgG constant domain Fc region to alter the effectorfunction(s) of the anti-transferrin receptor antibody. The effectorligand to which affinity is altered can be, for example, an Fc receptoror the C1 component of complement. This approach is described in furtherdetail in U.S. Pat. Nos. 5,624,821 and 5,648,260. In some embodiments,the deletion or inactivation (through point mutations or other means) ofa constant region domain can reduce Fc receptor binding of thecirculating antibody thereby increasing tumor localization. See, e.g.,U.S. Pat. Nos. 5,585,097 and 8,591,886 for a description of mutationsthat delete or inactivate the constant domain and thereby increase tumorlocalization. In some embodiments, one or more amino acid substitutionsmay be introduced into the Fc region of an antibody described herein toremove potential glycosylation sites on Fc region, which may reduce Fcreceptor binding (see, e.g., Shields R L et al., (2001) J Biol Chem 276:6591-604).

In some embodiments, one or more amino in the constant region of amuscle-targeting antibody described herein can be replaced with adifferent amino acid residue such that the antibody has altered Clqbinding and/or (e.g., and) reduced or abolished complement dependentcytotoxicity (CDC). This approach is described in further detail in U.S.Pat. No. 6,194,551 (Idusogie et al). In some embodiments, one or moreamino acid residues in the N-terminal region of the CH2 domain of anantibody described herein are altered to thereby alter the ability ofthe antibody to fix complement. This approach is described further inInternational Publication No. WO 94/29351. In some embodiments, the Fcregion of an antibody described herein is modified to increase theability of the antibody to mediate antibody dependent cellularcytotoxicity (ADCC) and/or (e.g., and) to increase the affinity of theantibody for an Fcγ receptor. This approach is described further inInternational Publication No. WO 00/42072.

In some embodiments, the heavy and/or (e.g., and) light chain variabledomain(s) sequence(s) of the antibodies provided herein can be used togenerate, for example, CDR-grafted, chimeric, humanized, or compositehuman antibodies or antigen-binding fragments, as described elsewhereherein. As understood by one of ordinary skill in the art, any variant,CDR-grafted, chimeric, humanized, or composite antibodies derived fromany of the antibodies provided herein may be useful in the compositionsand methods described herein and will maintain the ability tospecifically bind transferrin receptor, such that the variant,CDR-grafted, chimeric, humanized, or composite antibody has at least50%, at least 60%, at least 70%, at least 80%, at least 90%, at least95% or more binding to transferrin receptor relative to the originalantibody from which it is derived.

In some embodiments, the antibodies provided herein comprise mutationsthat confer desirable properties to the antibodies. For example, toavoid potential complications due to Fab-arm exchange, which is known tooccur with native IgG4 mAbs, the antibodies provided herein may comprisea stabilizing ‘Adair’ mutation (Angal S., et al., “A single amino acidsubstitution abolishes the heterogeneity of chimeric mouse/human (IgG4)antibody,” Mol Immunol 30, 105-108; 1993), where serine 228 (EUnumbering; residue 241 Kabat numbering) is converted to prolineresulting in an IgG1-like hinge sequence. Accordingly, any of theantibodies may include a stabilizing ‘Adair’ mutation.

As provided herein, antibodies of this disclosure may optionallycomprise constant regions or parts thereof. For example, a VL domain maybe attached at its C-terminal end to a light chain constant domain likeCκ or Cλ. Similarly, a VH domain or portion thereof may be attached toall or part of a heavy chain like IgA, IgD, IgE, IgG, and IgM, and anyisotype subclass. Antibodies may include suitable constant regions (see,for example, Kabat et al., Sequences of Proteins of ImmunologicalInterest, No. 91-3242, National Institutes of Health Publications,Bethesda, Md. (1991)). Therefore, antibodies within the scope of thismay disclosure include VH and VL domains, or an antigen binding portionthereof, combined with any suitable constant regions.

ii. Muscle-Targeting Peptides

Some aspects of the disclosure provide muscle-targeting peptides asmuscle-targeting agents. Short peptide sequences (e.g., peptidesequences of 5-20 amino acids in length) that bind to specific celltypes have been described. For example, cell-targeting peptides havebeen described in Vines e., et al., A. “Cell-penetrating andcell-targeting peptides in drug delivery” Biochim Biophys Acta 2008,1786: 126-38; Jarver P., et al., “In vivo biodistribution and efficacyof peptide mediated delivery” Trends Pharmacol Sci 2010; 31: 528-35;Samoylova T. I., et al., “Elucidation of muscle-binding peptides byphage display screening” Muscle Nerve 1999; 22: 460-6; U.S. Pat. No.6,329,501, issued on Dec. 11, 2001, entitled “METHODS AND COMPOSITIONSFOR TARGETING COMPOUNDS TO MUSCLE”; and Samoylov A. M., et al.,“Recognition of cell-specific binding of phage display derived peptidesusing an acoustic wave sensor.” Biomol Eng 2002; 18: 269-72; the entirecontents of each of which are incorporated herein by reference. Bydesigning peptides to interact with specific cell surface antigens(e.g., receptors), selectivity for a desired tissue, e.g., muscle, canbe achieved. Skeletal muscle-targeting has been investigated and a rangeof molecular payloads are able to be delivered. These approaches mayhave high selectivity for muscle tissue without many of the practicaldisadvantages of a large antibody or viral particle. Accordingly, insome embodiments, the muscle-targeting agent is a muscle-targetingpeptide that is from 4 to 50 amino acids in length. In some embodiments,the muscle-targeting peptide is 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32,33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or50 amino acids in length. Muscle-targeting peptides can be generatedusing any of several methods, such as phage display.

In some embodiments, a muscle-targeting peptide may bind to aninternalizing cell surface receptor that is overexpressed or relativelyhighly expressed in muscle cells, e.g. a transferrin receptor, comparedwith certain other cells. In some embodiments, a muscle-targetingpeptide may target, e.g., bind to, a transferrin receptor. In someembodiments, a peptide that targets a transferrin receptor may comprisea segment of a naturally occurring ligand, e.g., transferrin. In someembodiments, a peptide that targets a transferrin receptor is asdescribed in U.S. Pat. No. 6,743,893, filed Nov. 30, 2000,“RECEPTOR-MEDIATED UPTAKE OF PEPTIDES THAT BIND THE HUMAN TRANSFERRINRECEPTOR”. In some embodiments, a peptide that targets a transferrinreceptor is as described in Kawamoto, M. et al, “A novel transferrinreceptor-targeted hybrid peptide disintegrates cancer cell membrane toinduce rapid killing of cancer cells.” BMC Cancer. 2011 Aug. 18; 11:359.In some embodiments, a peptide that targets a transferrin receptor is asdescribed in U.S. Pat. No. 8,399,653, filed May 20, 2011,“TRANSFERRIN/TRANSFERRIN RECEPTOR-MEDIATED SIRNA DELIVERY”.

As discussed above, examples of muscle targeting peptides have beenreported. For example, muscle-specific peptides were identified usingphage display library presenting surface heptapeptides. As one example apeptide having the amino acid sequence ASSLNIA (SEQ ID NO: 138) bound toC2C12 murine myotubes in vitro, and bound to mouse muscle tissue invivo. Accordingly, in some embodiments, the muscle-targeting agentcomprises the amino acid sequence ASSLNIA (SEQ ID NO: 138). This peptidedisplayed improved specificity for binding to heart and skeletal muscletissue after intravenous injection in mice with reduced binding toliver, kidney, and brain. Additional muscle-specific peptides have beenidentified using phage display. For example, a 12 amino acid peptide wasidentified by phage display library for muscle targeting in the contextof treatment for DMD. See, Yoshida D., et al., “Targeting of salicylateto skin and muscle following topical injections in rats.” Int J Pharm2002; 231: 177-84; the entire contents of which are hereby incorporatedby reference. Here, a 12 amino acid peptide having the sequenceSKTFNTHPQSTP (SEQ ID NO: 139) was identified and this muscle-targetingpeptide showed improved binding to C2C12 cells relative to the ASSLNIA(SEQ ID NO: 138) peptide.

An additional method for identifying peptides selective for muscle(e.g., skeletal muscle) over other cell types includes in vitroselection, which has been described in Ghosh D., et al., “Selection ofmuscle-binding peptides from context-specific peptide-presenting phagelibraries for adenoviral vector targeting” J Virol 2005; 79: 13667-72;the entire contents of which are incorporated herein by reference. Bypre-incubating a random 12-mer peptide phage display library with amixture of non-muscle cell types, non-specific cell binders wereselected out. Following rounds of selection the 12 amino acid peptideTARGEHKEEELI (SEQ ID NO: 140) appeared most frequently. Accordingly, insome embodiments, the muscle-targeting agent comprises the amino acidsequence TARGEHKEEELI (SEQ ID NO: 140).

A muscle-targeting agent may an amino acid-containing molecule orpeptide. A muscle-targeting peptide may correspond to a sequence of aprotein that preferentially binds to a protein receptor found in musclecells. In some embodiments, a muscle-targeting peptide contains a highpropensity of hydrophobic amino acids, e.g. valine, such that thepeptide preferentially targets muscle cells. In some embodiments, amuscle-targeting peptide has not been previously characterized ordisclosed. These peptides may be conceived of, produced, synthesized,and/or (e.g., and) derivatized using any of several methodologies, e.g.phage displayed peptide libraries, one-bead one-compound peptidelibraries, or positional scanning synthetic peptide combinatoriallibraries. Exemplary methodologies have been characterized in the artand are incorporated by reference (Gray, B. P. and Brown, K. C.“Combinatorial Peptide Libraries: Mining for Cell-Binding Peptides” ChemRev. 2014, 114:2, 1020-1081.; Samoylova, T. I. and Smith, B. F.“Elucidation of muscle-binding peptides by phage display screening.”Muscle Nerve, 1999, 22:4. 460-6.). In some embodiments, amuscle-targeting peptide has been previously disclosed (see, e.g. WriterM. J. et al. “Targeted gene delivery to human airway epithelial cellswith synthetic vectors incorporating novel targeting peptides selectedby phage display.” J. Drug Targeting. 2004; 12:185; Cal, D.“BDNF-mediated enhancement of inflammation and injury in the agingheart.” Physiol Genomics. 2006, 24:3, 191-7.; Zhang, L. “Molecularprofiling of heart endothelial cells.” Circulation, 2005, 112:11,1601-11.; McGuire, M. J. et al. “In vitro selection of a peptide withhigh selectivity for cardiomyocytes in vivo.” J Mol Biol. 2004, 342:1,171-82.). Exemplary muscle-targeting peptides comprise an amino acidsequence of the following group: CQAQGQLVC (SEQ ID NO: 141), CSERSMNFC(SEQ ID NO: 142), CPKTRRVPC (SEQ ID NO: 143), WLSEAGPVVTVRALRGTGSW (SEQID NO: 144), ASSLNIA (SEQ ID NO: 138), CMQHSMRVC (SEQ ID NO: 145), andDDTRHWG (SEQ ID NO: 146). In some embodiments, a muscle-targetingpeptide may comprise about 2-25 amino acids, about 2-20 amino acids,about 2-15 amino acids, about 2-10 amino acids, or about 2-5 aminoacids. Muscle-targeting peptides may comprise naturally-occurring aminoacids, e.g. cysteine, alanine, or non-naturally-occurring or modifiedamino acids. Non-naturally occurring amino acids include (3-amino acids,homo-amino acids, proline derivatives, 3-substituted alaninederivatives, linear core amino acids, N-methyl amino acids, and othersknown in the art. In some embodiments, a muscle-targeting peptide may belinear; in other embodiments, a muscle-targeting peptide may be cyclic,e.g. bicyclic (see, e.g. Silvana, M. G. et al. Mol. Therapy, 2018, 26:1,132-147.).

iii. Muscle-Targeting Receptor Ligands

A muscle-targeting agent may be a ligand, e.g. a ligand that binds to areceptor protein. A muscle-targeting ligand may be a protein, e.g.transferrin, which binds to an internalizing cell surface receptorexpressed by a muscle cell. Accordingly, in some embodiments, themuscle-targeting agent is transferrin, or a derivative thereof thatbinds to a transferrin receptor. A muscle-targeting ligand mayalternatively be a small molecule, e.g. a lipophilic small molecule thatpreferentially targets muscle cells relative to other cell types.Exemplary lipophilic small molecules that may target muscle cellsinclude compounds comprising cholesterol, cholesteryl, stearic acid,palmitic acid, oleic acid, oleyl, linolene, linoleic acid, myristicacid, sterols, dihydrotestosterone, testosterone derivatives, glycerine,alkyl chains, trityl groups, and alkoxy acids.

iv. Muscle-Targeting Aptamers

A muscle-targeting agent may be an aptamer, e.g. an RNA aptamer, whichpreferentially targets muscle cells relative to other cell types. Insome embodiments, a muscle-targeting aptamer has not been previouslycharacterized or disclosed. These aptamers may be conceived of,produced, synthesized, and/or (e.g., and) derivatized using any ofseveral methodologies, e.g. Systematic Evolution of Ligands byExponential Enrichment. Exemplary methodologies have been characterizedin the art and are incorporated by reference (Yan, A. C. and Levy, M.“Aptamers and aptamer targeted delivery” RNA biology, 2009, 6:3,316-20.; Germer, K. et al. “RNA aptamers and their therapeutic anddiagnostic applications.” Int. J. Biochem. Mol. Biol. 2013; 4: 27-40.).In some embodiments, a muscle-targeting aptamer has been previouslydisclosed (see, e.g. Phillippou, S. et al. “Selection and Identificationof Skeletal-Muscle-Targeted RNA Aptamers.” Mol Ther Nucleic Acids. 2018,10:199-214.; Thiel, W. H. et al. “Smooth Muscle Cell-targeted RNAAptamer Inhibits Neointimal Formation.” Mol Ther. 2016, 24:4, 779-87.).Exemplary muscle-targeting aptamers include the A01B RNA aptamer and RNAApt 14. In some embodiments, an aptamer is a nucleic acid-based aptamer,an oligonucleotide aptamer or a peptide aptamer. In some embodiments, anaptamer may be about 5-15 kDa, about 5-10 kDa, about 10-15 kDa, about1-5 Da, about 1-3 kDa, or smaller.

v. Other Muscle-Targeting Agents

One strategy for targeting a muscle cell (e.g., a skeletal muscle cell)is to use a substrate of a muscle transporter protein, such as atransporter protein expressed on the sarcolemma. In some embodiments,the muscle-targeting agent is a substrate of an influx transporter thatis specific to muscle tissue. In some embodiments, the influxtransporter is specific to skeletal muscle tissue. Two main classes oftransporters are expressed on the skeletal muscle sarcolemma, (1) theadenosine triphosphate (ATP) binding cassette (ABC) superfamily, whichfacilitate efflux from skeletal muscle tissue and (2) the solute carrier(SLC) superfamily, which can facilitate the influx of substrates intoskeletal muscle. In some embodiments, the muscle-targeting agent is asubstrate that binds to an ABC superfamily or an SLC superfamily oftransporters. In some embodiments, the substrate that binds to the ABCor SLC superfamily of transporters is a naturally-occurring substrate.In some embodiments, the substrate that binds to the ABC or SLCsuperfamily of transporters is a non-naturally occurring substrate, forexample, a synthetic derivative thereof that binds to the ABC or SLCsuperfamily of transporters.

In some embodiments, the muscle-targeting agent is a substrate of an SLCsuperfamily of transporters. SLC transporters are either equilibrativeor use proton or sodium ion gradients created across the membrane todrive transport of substrates. Exemplary SLC transporters that have highskeletal muscle expression include, without limitation, the SATTtransporter (ASCT1; SLC1A4), GLUT4 transporter (SLC2A4), GLUT7transporter (GLUT7; SLC2A7), ATRC2 transporter (CAT-2; SLC7A2), LAT3transporter (KIAA0245; SLC7A6), PHT1 transporter (PTR4; SLC15A4), OATP-Jtransporter (OATP5A1; SLC21A15), OCT3 transporter (EMT; SLC22A3), OCTN2transporter (FLJ46769; SLC22A5), ENT transporters (ENT1; SLC29A1 andENT2; SLC29A2), PAT2 transporter (SLC36A2), and SAT2 transporter(KIAA1382; SLC38A2). These transporters can facilitate the influx ofsubstrates into skeletal muscle, providing opportunities for muscletargeting.

In some embodiments, the muscle-targeting agent is a substrate of anequilibrative nucleoside transporter 2 (ENT2) transporter. Relative toother transporters, ENT2 has one of the highest mRNA expressions inskeletal muscle. While human ENT2 (hENT2) is expressed in most bodyorgans such as brain, heart, placenta, thymus, pancreas, prostate, andkidney, it is especially abundant in skeletal muscle. Human ENT2facilitates the uptake of its substrates depending on theirconcentration gradient. ENT2 plays a role in maintaining nucleosidehomeostasis by transporting a wide range of purine and pyrimidinenucleobases. The hENT2 transporter has a low affinity for allnucleosides (adenosine, guanosine, uridine, thymidine, and cytidine)except for inosine. Accordingly, in some embodiments, themuscle-targeting agent is an ENT2 substrate. Exemplary ENT2 substratesinclude, without limitation, inosine, 2′,3′-dideoxyinosine, andcalofarabine. In some embodiments, any of the muscle-targeting agentsprovided herein are associated with a molecular payload (e.g.,oligonucleotide payload). In some embodiments, the muscle-targetingagent is covalently linked to the molecular payload. In someembodiments, the muscle-targeting agent is non-covalently linked to themolecular payload.

In some embodiments, the muscle-targeting agent is a substrate of anorganic cation/carnitine transporter (OCTN2), which is a sodiumion-dependent, high affinity carnitine transporter. In some embodiments,the muscle-targeting agent is carnitine, mildronate, acetylcarnitine, orany derivative thereof that binds to OCTN2. In some embodiments, thecarnitine, mildronate, acetylcarnitine, or derivative thereof iscovalently linked to the molecular payload (e.g., oligonucleotidepayload).

A muscle-targeting agent may be a protein that is protein that exists inat least one soluble form that targets muscle cells. In someembodiments, a muscle-targeting protein may be hemojuvelin (also knownas repulsive guidance molecule C or hemochromatosis type 2 protein), aprotein involved in iron overload and homeostasis. In some embodiments,hemojuvelin may be full length or a fragment, or a mutant with at least75%, at least 80%, at least 85%, at least 90%, at least 95%, at least98% or at least 99% sequence identity to a functional hemojuvelinprotein. In some embodiments, a hemojuvelin mutant may be a solublefragment, may lack a N-terminal signaling, and/or (e.g., and) lack aC-terminal anchoring domain. In some embodiments, hemojuvelin may beannotated under GenBank RefSeq Accession Numbers NM_001316767.1,NM_145277.4, NM_202004.3, NM_213652.3, or NM_213653.3. It should beappreciated that a hemojuvelin may be of human, non-human primate, orrodent origin.

B. Molecular Payloads

Some aspects of the disclosure provide molecular payloads, e.g., formodulating a biological outcome, e.g., the transcription of a DNAsequence, the expression of a protein, or the activity of a protein. Insome embodiments, a molecular payload is linked to, or otherwiseassociated with a muscle-targeting agent. In some embodiments, suchmolecular payloads are capable of targeting to a muscle cell, e.g., viaspecifically binding to a nucleic acid or protein in the muscle cellfollowing delivery to the muscle cell by an associated muscle-targetingagent. It should be appreciated that various types of muscle-targetingagents may be used in accordance with the disclosure. For example, themolecular payload may comprise, or consist of, an oligonucleotide (e.g.,antisense oligonucleotide), a peptide (e.g., a peptide that binds anucleic acid or protein associated with disease in a muscle cell), aprotein (e.g., a protein that binds a nucleic acid or protein associatedwith disease in a muscle cell), or a small molecule (e.g., a smallmolecule that modulates the function of a nucleic acid or proteinassociated with disease in a muscle cell). In some embodiments, themolecular payload is an oligonucleotide that comprises a strand having aregion of complementarity to a DUX4. In some embodiments, the molecularpayload is a DNA decoy, e.g., of a DUX4 nucleic acid. Exemplarymolecular payloads are described in further detail herein, however, itshould be appreciated that the exemplary molecular payloads providedherein are not meant to be limiting.

i. Oligonucleotides

Any suitable oligonucleotide may be used as a molecular payload, asdescribed herein. In some embodiments, the oligonucleotide may bedesigned to cause degradation of an mRNA (e.g., the oligonucleotide maybe a gapmer, an siRNA, a ribozyme or an aptamer that causesdegradation). In some embodiments, the oligonucleotide may be designedto block translation of an mRNA (e.g., the oligonucleotide may be amixmer, an siRNA or an aptamer that blocks translation). In someembodiments, an oligonucleotide may be designed to cause degradation andblock translation of an mRNA. In some embodiments, an oligonucleotidemay be a guide nucleic acid (e.g., guide RNA) for directing activity ofan enzyme (e.g., a gene editing enzyme). Other examples ofoligonucleotides are provided herein. It should be appreciated that, insome embodiments, oligonucleotides in one format (e.g., antisenseoligonucleotides) may be suitably adapted to another format (e.g., siRNAoligonucleotides) by incorporating functional sequences (e.g., antisensestrand sequences) from one format to the other format.

Any suitable oligonucleotide may be used as a molecular payload, asdescribed herein. Examples of oligonucleotides useful for targeting DUX4are provided in U.S. Pat. No. 9,988,628, published on Feb. 2, 2017,entitled “AGENTS USEFUL IN TREATING FACIOSCAPULOHUMERAL MUSCULARDYSTROPHY”; U.S. Pat. No. 9,469,851, published Oct. 30, 2014, entitled“RECOMBINANT VIRUS PRODUCTS AND METHODS FOR INHIBITING EXPRESSION OFDUX4”; US Patent Application Publication 20120225034, published on Sep.6, 2012, entitled “AGENTS USEFUL IN TREATING FACIOSCAPULOHUMERALMUSCULAR DYSTROPHY”; PCT Patent Application Publication Number WO2013/120038, published on Aug. 15, 2013, entitled “MORPHOLINO TARGETINGDUX4 FOR TREATING FSHD”; Chen et al., “Morpholino-mediated Knockdown ofDUX4 Toward Facioscapulohumeral Muscular Dystrophy Therapeutics,”Molecular Therapy, 2016, 24:8, 1405-1411.; and Ansseau et al.,“Antisense Oligonucleotides Used to Target the DUX4 mRNA as TherapeuticApproaches in Facioscapulohumeral Muscular Dystrophy (FSHD),” Genes,2017, 8, 93; the contents of each of which are incorporated herein intheir entireties. In some embodiments, the oligonucleotide is anantisense oligonucleotide, a morpholino, a siRNA, a shRNA, or anotheroligonucleotide which hybridizes with the target DUX4 gene or mRNA.

In some embodiments, oligonucleotides may have a region ofcomplementarity to a sequence as set forth as: Human DUX4, correspondingto NCBI sequence NM_001293798.1 (SEQ ID NO: 147), NM_001293798.2 (SEQ IDNO: 157), and/or (e.g., and) NM_001306068.3 (SEQ ID NO: 158): as belowand/or (e.g., and) Mouse DUX4, corresponding to NCBI sequenceNM_001081954.1 (SEQ ID NO: 148), as below. In some embodiments, theoligonucleotide may have a region of complementarity to ahypomethylated, contracted D4Z4 repeat, as in Daxinger, et al., “Geneticand Epigenetic Contributors to FSHD,” published in Curr Opin Genet Devin 2015, Lim J-W, et al., DICER/AGO-dependent epigenetic silencing ofD4Z4 repeats enhanced by exogenous siRNA suggests mechanisms andtherapies for FSHD Hum Mol Genet. 2015 Sep. 1; 24(17): 4817-4828, thecontents of each of which are incorporated in their entireties.

In some embodiments, oligonucleotides may have a region ofcomplementarity to a sequence set forth as follows, which is an examplehuman DUX4 gene sequence (NM_001293798.1) (SEQ ID NO: 147):

ATGGCCCTCCCGACACCCTCGGACAGCACCCTCCCCGCGGAAGCCCGGGGACGAGGACGGCGACGGAGACTCGTTTGGACCCCGAGCCAAAGCGAGGCCCTGCGAGCCTGCTTTGAGCGGAACCCGTACCCGGGCATCGCCACCAGAGAACGGCTGGCCCAGGCCATCGGCATTCCGGAGCCCAGGGTCCAGATTTGGTTTCAGAATGAGAGGTCACGCCAGCTGAGGCAGCACCGGCGGGAATCTCGGCCCTGGCCCGGGAGACGCGGCCCGCCAGAAGGCCGGCGAAAGCGGACCGCCGTCACCGGATCCCAGACCGCCCTGCTCCTCCGAGCCTTTGAGAAGGATCGCTTTCCAGGCATCGCCGCCCGGGAGGAGCTGGCCAGAGAGACGGGCCTCCCGGAGTCCAGGATTCAGATCTGGTTTCAGAATCGAAGGGCCAGGCACCCGGGACAGGGTGGCAGGGCGCCCGCGCAGGCAGGCGGCCTGTGCAGCGCGGCCCCCGGCGGGGGTCACCCTGCTCCCTCGTGGGTCGCCTTCGCCCACACCGGCGCGTGGGGAACGGGGCTTCCCGCACCCCACGTGCCCTGCGCGCCTGGGGCTCTCCCACAGGGGGCTTTCGTGAGCCAGGCAGCGAGGGCCGCCCCCGCGCTGCAGCCCAGCCAGGCCGCGCCGGCAGAGGGGATCTCCCAACCTGCCCCGGCGCGCGGGGATTTCGCCTACGCCGCCCCGGCTCCTCCGGACGGGGCGCTCTCCCACCCTCAGGCTCCTCGGTGGCCTCCGCACCCGGGCAAAAGCCGGGAGGACCGGGACCCGCAGCGCGACGGCCTGCCGGGCCCCTGCGCGGTGGCACAGCCTGGGCCCGCTCAAGCGGGGCCGCAGGGCCAAGGGGTGCTTGCGCCACCCACGTCCCAGGGGAGTCCGTGGTGGGGCTGGGGCCGGGGTCCCCAGGTCGCCGGGGCGGCGTGGGAACCCCAAGCCGGGGCAGCTCCACCTCCCCAGCCCGCGCCCCCGGACGCCTCCGCCTCCGCGCGGCAGGGGCAGATGCAAGGCATCCCGGCGCCCTCCCAGGCGCTCCAGGAGCCGGCGCCCTGGTCTGCACTCCCCTGCGGCCTGCTGCTGGATGAGCTCCTGGCGAGCCCGGAGTTTCTGCAGCAGGCGCAACCTCTCCTAGAAACGGAGGCCCCGGGGGAGCTGGAGGCCTCGGAAGAGGCCGCCTCGCTGGAAGCACCCCTCAGCGAGGAAGAATACCGGGCTCTGCTGGAGGAGCTTTAG

In some embodiments, oligonucleotides may have a region ofcomplementarity to a sequence set forth as follows, which is an examplehuman DUX4 gene sequence (NM_001293798.2) (SEQ ID NO: 157):

ATGGCCCTCCCGACACCCTCGGACAGCACCCTCCCCGCGGAAGCCCGGGGACGAGGACGGCGACGGAGACTCGTTTGGACCCCGAGCCAAAGCGAGGCCCTGCGAGCCTGCTTTGAGCGGAACCCGTACCCGGGCATCGCCACCAGAGAACGGCTGGCCCAGGCCATCGGCATTCCGGAGCCCAGGGTCCAGATTTGGTTTCAGAATGAGAGGTCACGCCAGCTGAGGCAGCACCGGCGGGAATCTCGGCCCTGGCCCGGGAGACGCGGCCCGCCAGAAGGCCGGCGAAAGCGGACCGCCGTCACCGGATCCCAGACCGCCCTGCTCCTCCGAGCCTTTGAGAAGGATCGCTTTCCAGGCATCGCCGCCCGGGAGGAGCTGGCCAGAGAGACGGGCCTCCCGGAGTCCAGGATTCAGATCTGGTTTCAGAATCGAAGGGCCAGGCACCCGGGACAGGGTGGCAGGGCGCCCGCGCAGGCAGGCGGCCTGTGCAGCGCGGCCCCCGGCGGGGGTCACCCTGCTCCCTCGTGGGTCGCCTTCGCCCACACCGGCGCGTGGGGAACGGGGCTTCCCGCACCCCACGTGCCCTGCGCGCCTGGGGCTCTCCCACAGGGGGCTTTCGTGAGCCAGGCAGCGAGGGCCGCCCCCGCGCTGCAGCCCAGCCAGGCCGCGCCGGCAGAGGGGATCTCCCAACCTGCCCCGGCGCGCGGGGATTTCGCCTACGCCGCCCCGGCTCCTCCGGACGGGGCGCTCTCCCACCCTCAGGCTCCTCGCTGGCCTCCGCACCCGGGCAAAAGCCGGGAGGACCGGGACCCGCAGCGCGACGGCCTGCCGGGCCCCTGCGCGGTGGCACAGCCTGGGCCCGCTCAAGCGGGGCCGCAGGGCCAAGGGGTGCTTGCGCCACCCACGTCCCAGGGGAGTCCGTGGTGGGGCTGGGGCCGGGGTCCCCAGGTCGCCGGGGCGGCGTGGGAACCCCAAGCCGGGGCAGCTCCACCTCCCCAGCCCGCGCCCCCGGACGCCTCCGCCTCCGCGCGGCAGGGGCAGATGCAAGGCATCCCGGCGCCCTCCCAGGCGCTCCAGGAGCCGGCGCCCTGGTCTGCACTCCCCTGCGGCCTGCTGCTGGATGAGCTCCTGGCGAGCCCGGAGTTTCTGCAGCAGGCGCAACCTCTCCTAGAAACGGAGGCCCCGGGGGAGCTGGAGGCCTCGGAAGAGGCCGCCTCGCTGGAAGCACCCCTCAGCGAGGAAGAATACCGGGCTCTGCTGGAGGAGCTTTAGGACGCGGGGTCTAGGCCCGGTGAGAGACTCCACACCGCGGAGAACTGCCATTCTTTCCTGGGCATCCCGGGGATCCCAGAGCCGGCCCAGGTACCAGCAGACCTGCGCGCAGTGCGCACCCCGGCTGACGTGCAAGGGAGCTCGCTGGCCTCTCTGTGCCCTTGTTCTTCCGTGAAATTCTGGCTGAATGTCTCCCCCCACCTTCCGACGCTGTCTAGGCAAACCTGGATTAGAGTTACATCTCCTGGATGATTAGTTCAGAGATATATTAAAATGCCCCCTCCCTGTGGATCCTATAG.

In some embodiments, oligonucleotides may have a region ofcomplementarity to a sequence set forth as follows, which is an examplehuman DUX4 gene sequence (NM_001306068.3) (SEQ ID NO: 158):

ATGGCCCTCCCGACACCCTCGGACAGCACCCTCCCCGCGGAAGCCCGGGGACGAGGACGGCGACGGAGACTCGTTTGGACCCCGAGCCAAAGCGAGGCCCTGCGAGCCTGCTTTGAGCGGAACCCGTACCCGGGCATCGCCACCAGAGAACGGCTGGCCCAGGCCATCGGCATTCCGGAGCCCAGGGTCCAGATTTGGTTTCAGAATGAGAGGTCACGCCAGCTGAGGCAGCACCGGCGGGAATCTCGGCCCTGGCCCGGGAGACGCGGCCCGCCAGAAGGCCGGCGAAAGCGGACCGCCGTCACCGGATCCCAGACCGCCCTGCTCCTCCGAGCCTTTGAGAAGGATCGCTTTCCAGGCATCGCCGCCCGGGAGGAGCTGGCCAGAGAGACGGGCCTCCCGGAGTCCAGGATTCAGATCTGGTTTCAGAATCGAAGGGCCAGGCACCCGGGACAGGGTGGCAGGGCGCCCGCGCAGGCAGGCGGCCTGTGCAGCGCGGCCCCCGGCGGGGGTCACCCTGCTCCCTCGTGGGTCGCCTTCGCCCACACCGGCGCGTGGGGAACGGGGCTTCCCGCACCCCACGTGCCCTGCGCGCCTGGGGCTCTCCCACAGGGGGCTTTCGTGAGCCAGGCAGCGAGGGCCGCCCCCGCGCTGCAGCCCAGCCAGGCCGCGCCGGCAGAGGGGATCTCCCAACCTGCCCCGGCGCGCGGGGATTTCGCCTACGCCGCCCCGGCTCCTCCGGACGGGGCGCTCTCCCACCCTCAGGCTCCTCGGTGGCCTCCGCACCCGGGCAAAAGCCGGGAGGACCGGGACCCGCAGCGCGACGGCCTGCCGGGCCCCTGCGCGGTGGCACAGCCTGGGCCCGCTCAAGCGGGGCCGCAGGGCCAAGGGGTGCTTGCGCCACCCACGTCCCAGGGGAGTCCGTGGTGGGGCTGGGGCCGGGGTCCCCAGGTCGCCGGGGCGGCGTGGGAACCCCAAGCCGGGGCAGCTCCACCTCCCCAGCCCGCGCCCCCGGACGCCTCCGCCTCCGCGCGGCAGGGGCAGATGCAAGGCATCCCGGCGCCCTCCCAGGCGCTCCAGGAGCCGGCGCCCTGGTCTGCACTCCCCTGCGGCCTGCTGCTGGATGAGCTCCTGGCGAGCCCGGAGTTTCTGCAGCAGGCGCAACCTCTCCTAGAAACGGAGGCCCCGGGGGAGCTGGAGGCCTCGGAAGAGGCCGCCTCGCTGGAAGCACCCCTCAGCGAGGAAGAATACCGGGCTCTGCTGGAGGAGCTTTAGGACGCGGGGTTGGGACGGGGTCGGGTGGTTCGGGGCAGGGCGGTGGCCTCTCTTTCGCGGGGAACACCTGGCTGGCTACGGAGGGGCGTGTCTCCGCCCCGCCCCCTCCACCGGGCTGACCGGCCTGGGATTCCTGCCTTCTAGGTCTAGGCCCGGTGAGAGACTCCACTCCGCGGAGAACTGCCTTTCTTTCCTGGGCATCCCGGGGATCCCAGAGCCGGCCCAGGTACCAGCAGACCTGCGCGCAGTGCGCACCCCGGCTGACGTGCAAGGGAGCTCGCTGGCCTCTCTGTGCCCTTGTTCTTCCGTGAAATTCTGGCTGAATGTCTCCCCCCACCTTCCGACGCTGTCTAGGCAAACCTGGATTAGAGTTACATCTCCTGGATGATTAGTTCAGAGATATATTAAAATGCCCCCTCCCTGTG GATCCTATAG.In some embodiments, oligonucleotides may have a region ofcomplementarity to a sequence set forth as follows, which is an examplemouse DUX4 gene sequence (SEQ ID NO: 148) (NM_001081954.1):

ATGGCAGAAGCTGGCAGCCCTGTTGGTGGCAGTGGTGTGGCACGGGAATCCCGGCGGCGCAGGAAGACGGTTTGGCAGGCCTGGCAAGAGCAGGCCCTGCTATCAACTTTCAAGAAGAAGAGATACCTGAGCTTCAAGGAGAGGAAGGAGCTGGCCAAGCGAATGGGGGTCTCAGATTGCCGCATCCGCGTGTGGTTTCAGAACCGCAGGAATCGCAGTGGAGAGGAGGGGCATGCCTCAAAGAGGTCCATCAGAGGCTCCAGGCGGCTAGCCTCGCCACAGCTCCAGGAAGAGCTTGGATCCAGGCCACAGGGTAGAGGCATGCGCTCATCTGGCAGAAGGCCTCGCACTCGACTCACCTCGCTACAGCTCAGGATCCTAGGGCAAGCCTTTGAGAGGAACCCACGACCAGGCTTTGCTACCAGGGAGGAGCTGGCGCGTGACACAGGGTTGCCCGAGGACACGATCCACATATGGTTTCAAAACCGAAGAGCTCGGCGGCGCCACAGGAGGGGCAGGCCCACAGCTCAAGATCAAGACTTGCTGGCGTCACAAGGGTCGGATGGGGCCCCTGCAGGTCCGGAAGGCAGAGAGCGTGAAGGTGCCCAGGAGAACTTGTTGCCACAGGAAGAAGCAGGAAGTACGGGCATGGATACCTCGAGCCCTAGCGACTTGCCCTCCTTCTGCGGAGAGTCCCAGCCTTTCCAAGTGGCACAGCCCCGTGGAGCAGGCCAACAAGAGGCCCCCACTCGAGCAGGCAACGCAGGCTCTCTGGAACCCCTCCTTGATCAGCTGCTGGATGAAGTCCAAGTAGAAGAGCCTGCTCCAGCCCCTCTGAATTTGGATGGAGACCCTGGTGGCAGGGTGCATGAAGGTTCCCAGGAGAGCTTTTGGCCACAGGAAGAAGCAGGAAGTACAGGCATGGATACTTCTAGCCCCAGCGACTCAAACTCCTTCTGCAGAGAGTCCCAGCCTTCCCAAGTGGCACAGCCCTGTGGAGCGGGCCAAGAAGATGCCCGCACTCAAGCAGACAGCACAGGCCCTCTGGAACTCCTCCTCCTTGATCAACTGCTGGACGAAGTCCAAAAGGAAGAGCATGTGCCAGTCCCACTGGATTGGGGTAGAAATCCTGGCAGCAGGGAGCATGAAGGTTCCCAGGACAGCTTACTGCCCCTGGAGGAAGCAGTAAATTCGGGCATGGATACCTCGATCCCTAGCATCTGGCCAACCTTCTGCAGAGAATCCCAGCCTCCCCAAGTGGCACAGCCCTCTGGACCAGGCCAAGCACAGGCCCCCACTCAAGGTGGGAACACGGACCCCCTGGAGCTCTTCCTCTATCAACTGTTGGATGAAGTCCAAGTAGAAGAGCATGCTCCAGCCCCTCTGAATTGGGATGTAGATCCTGGTGGCAGGGTGCATGAAGGTTCGTGGGAGAGCTTTTGGCCACAGGAAGAAGCAGGAAGTACAGGCCTGGATACTTCAAGCCCCAGCGACTCAAACTCCTTCTTCAGAGAGTCCAAGCCTTCCCAAGTGGCACAGCGCCGTGGAGCGGGCCAAGAAGATGCCCGCACTCAAGCAGACAGCACAGGCCCTCTGGAACTCCTCCTCTTTGATCAACTGCTGGACGAAGTCCAAAAGGAAGAGCATGTGCCAGCCCCACTGGATTGGGGTAGAAATCCTGGCAGCATGGAGCATGAAGGTTCCCAGGACAGCTTACTGCCCCTGGAGGAAGCAGCAAATTCGGGCAGGGATACCTCGATCCCTAGCATCTGGCCAGCCTTCTGCAGAAAATCCCAGCCTCCCCAAGTGGCACAGCCCTCTGGACCAGGCCAAGCACAGGCCCCCATTCAAGGTGGGAACACGGACCCCCTGGAGCTCTTCCTTGATCAACTGCTGACCGAAGTCCAACTTGAGGAGCAGGGGCCTGCCCCTGTGAATGTGGAGGAAACATGGGAGCAAATGGACACAACACCTATCTGCCTCTCACTTCAGAAGAATATCAGACTCTTCTAGATATGCTCTGA.

In some embodiments, an oligonucleotide may have a region ofcomplementarity to DUX4 gene sequences of multiple species, e.g.,selected from human, mouse and non-human species.

In some embodiments, an oligonucleotide that targets DUX4 is a FM10sequence. In some embodiments, an oligonucleotide that targets DUX4 is aphosphorodiamidate morpholino version of a FM10 sequence. In someembodiments, an oligonucleotide that targets DUX4 comprises the sequenceGGGCATTTTAATATATCTCTGAACT (SEQ ID NO: 151). In some embodiments, anoligonucleotide that targets DUX4 comprises a sequence that iscomplementary to at least 15 consecutive nucleotides of

(SEQ ID NO: 150)   AGTTCAGAGATATATTAAAATGCCC

In some embodiments, muscle specific E3 ubiquitin ligases areoverexpressed in FSHD and function in muscle atrophy (see, e.g.,Vanderplanck, C. et al. “The FSHD Atrophic Myotube Phenotype Is Causedby DUX4 Expression” PLoS One 6,10:e26820, 2011). In some embodiments,downregulation of these ligases presents a viable therapeutic strategy.In some embodiments, an oligonucleotide may target, e.g., inhibit theexpression of, a muscle specific E3 ubiquitin ligase implicated in FSHD,such as MuRF1 (also known as TRIM63) and MAFbx (also known as Fbx032).In some embodiments, an oligonucleotide may have a region ofcomplementarity to at least one MuRF1 gene sequence, e.g. human MuRF1(NCBI Gene ID 84676). In some embodiments, an oligonucleotide may have aregion of complementarity to at least one MAFbx gene sequence, e.g.human MAFbx (NCBI Gene ID 114907).

In some embodiments, any one of the oligonucleotides can be in saltform, e.g., as sodium, potassium, or magnesium salts.

In some embodiments, the 5′ or 3′ nucleoside (e.g., terminal nucleoside)of any one of the oligonucleotides described herein is conjugated to anamine group, optionally via a spacer. In some embodiments, the spacercomprises an aliphatic moiety. In some embodiments, the spacer comprisesa polyethylene glycol moiety. In some embodiments, a phosphodiesterlinkage is present between the spacer and the 5′ or 3′ nucleoside of theoligonucleotide. In some embodiments, the 5′ or 3′ nucleoside (e.g.,terminal nucleoside) of any of the oligonucleotides described herein isconjugated to a spacer that is a substituted or unsubstituted aliphatic,substituted or unsubstituted heteroaliphatic, substituted orunsubstituted carbocyclylene, substituted or unsubstitutedheterocyclylene, substituted or unsubstituted arylene, substituted orunsubstituted heteroarylene, —O—, —N(R^(A))—, —S—, —C(═O)—, —C(═O)O—,—C(═O)NR^(A)—, —NR^(A)C(═O)—, —NR^(A)C(═O)R^(A)—, —C(═O)R^(A)—,—NR^(A)C(═O)O—, —NR^(A)C(═O)N(R^(A))—, —OC(═O)—, —OC(═O)O—,—OC(═O)N(R^(A))—, —S(O)₂NR^(A)—, —NR^(A)S(O)₂—, or a combinationthereof; each R^(A) is independently hydrogen or substituted orunsubstituted alkyl. In certain embodiments, the spacer is a substitutedor unsubstituted alkylene, substituted or unsubstituted heterocyclylene,substituted or unsubstituted heteroarylene, —O—, —N(R^(A))—, or—C(═O)N(R^(A))₂, or a combination thereof.

In some embodiments, the 5′ or 3′ nucleoside of any one of theoligonucleotides described herein is conjugated to a compound of theformula —NH2-(CH₂)_(n)—, wherein n is an integer from 1 to 12. In someembodiments, n is 6, 7, 8, 9, 10, 11, or 12. In some embodiments, aphosphodiester linkage is present between the compound of the formulaNH₂—(CH₂)_(n)— and the 5′ or 3′ nucleoside of the oligonucleotide. Insome embodiments, a compound of the formula NH₂—(CH₂)₆— is conjugated tothe oligonucleotide via a reaction between 6-amino-1-hexanol(NH₂—(CH₂)₆—OH) and the 5′ phosphate of the oligonucleotide.

In some embodiments, the oligonucleotide is conjugated to a targetingagent, e.g., a muscle targeting agent such as an anti-TfR antibody,e.g., via the amine group.

a. Oligonucleotide Size/Sequence

Oligonucleotides may be of a variety of different lengths, e.g.,depending on the format. In some embodiments, an oligonucleotide is 7,8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,26, 27, 28, 29, 30, 35, 40, 45, 50, 75, or more nucleotides in length.In a some embodiments, the oligonucleotide is 8 to 50 nucleotides inlength, 8 to 40 nucleotides in length, 8 to 30 nucleotides in length, 10to 15 nucleotides in length, 10 to 20 nucleotides in length, 15 to 25nucleotides in length, 21 to 23 nucleotides in lengths, etc.

In some embodiments, a complementary nucleic acid sequence of anoligonucleotide for purposes of the present disclosure is specificallyhybridizable or specific for the target nucleic acid when binding of thesequence to the target molecule (e.g., mRNA) interferes with the normalfunction of the target (e.g., mRNA) to cause a loss of activity (e.g.,inhibiting translation) or expression (e.g., degrading a target mRNA)and there is a sufficient degree of complementarity to avoidnon-specific binding of the sequence to non-target sequences underconditions in which avoidance of non-specific binding is desired, e.g.,under physiological conditions in the case of in vivo assays ortherapeutic treatment, and in the case of in vitro assays, underconditions in which the assays are performed under suitable conditionsof stringency. Thus, in some embodiments, an oligonucleotide may be atleast 80%, at least 85%, at least 90%, at least 91%, at least 92%, atleast 93%, at least 94%, at least 95%, at least 96%, at least 97%, atleast 98%, at least 99% or 100% complementary to the consecutivenucleotides of an target nucleic acid. In some embodiments acomplementary nucleotide sequence need not be 100% complementary to thatof its target to be specifically hybridizable or specific for a targetnucleic acid.

In some embodiments, an oligonucleotide comprises region ofcomplementarity to a target nucleic acid that is in the range of 8 to15, 8 to 30, 8 to 40, or 10 to 50, or 5 to 50, or 5 to 40 nucleotides inlength. In some embodiments, a region of complementarity of anoligonucleotide to a target nucleic acid is 5, 6, 7, 8, 9, 10, 11, 12,13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30,31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48,49, or 50 nucleotides in length. In some embodiments, the region ofcomplementarity is complementary with at least 8 consecutive nucleotidesof a target nucleic acid. In some embodiments, an oligonucleotide maycontain 1, 2 or 3 base mismatches compared to the portion of theconsecutive nucleotides of target nucleic acid. In some embodiments theoligonucleotide may have up to 3 mismatches over 15 bases, or up to 2mismatches over 10 bases.

In some embodiments, the oligonucleotide is complementary (e.g., atleast 85% at least 90%, at least 95%, or 100%) to a target sequence ofany one of the oligonucleotides provided herein. In some embodiments,such target sequence is 100% complementary to the oligonucleotideprovided herein.

In some embodiments, any one or more of the thymine bases (T's) in anyone of the oligonucleotides provided herein may optionally be uracilbases (U's), and/or any one or more of the U's may optionally be T's.

b. Oligonucleotide Modifications:

The oligonucleotides described herein may be modified, e.g., comprise amodified sugar moiety, a modified internucleoside linkage, a modifiednucleotide and/or (e.g., and) combinations thereof. In addition, in someembodiments, oligonucleotides may exhibit one or more of the followingproperties: do not mediate alternative splicing; are not immunestimulatory; are nuclease resistant; have improved cell uptake comparedto unmodified oligonucleotides; are not toxic to cells or mammals; haveimproved endosomal exit internally in a cell; minimizes TLR stimulation;or avoid pattern recognition receptors. Any of the modified chemistriesor formats of oligonucleotides described herein can be combined witheach other. For example, one, two, three, four, five, or more differenttypes of modifications can be included within the same oligonucleotide.

In some embodiments, certain nucleotide modifications may be used thatmake an oligonucleotide into which they are incorporated more resistantto nuclease digestion than the native oligodeoxynucleotide oroligoribonucleotide molecules; these modified oligonucleotides surviveintact for a longer time than unmodified oligonucleotides. Specificexamples of modified oligonucleotides include those comprising modifiedbackbones, for example, modified internucleoside linkages such asphosphorothioates, phosphotriesters, methyl phosphonates, short chainalkyl or cycloalkyl intersugar linkages or short chain heteroatomic orheterocyclic intersugar linkages. Accordingly, oligonucleotides of thedisclosure can be stabilized against nucleolytic degradation such as bythe incorporation of a modification, e.g., a nucleotide modification.

In some embodiments, an oligonucleotide may be of up to 50 or up to 100nucleotides in length in which 2 to 10, 2 to 15, 2 to 16, 2 to 17, 2 to18, 2 to 19, 2 to 20, 2 to 25, 2 to 30, 2 to 40, 2 to 45, or morenucleotides of the oligonucleotide are modified nucleotides. Theoligonucleotide may be of 8 to 30 nucleotides in length in which 2 to10, 2 to 15, 2 to 16, 2 to 17, 2 to 18, 2 to 19, 2 to 20, 2 to 25, 2 to30 nucleotides of the oligonucleotide are modified nucleotides. Theoligonucleotide may be of 8 to 15 nucleotides in length in which 2 to 4,2 to 5, 2 to 6,2 to 7,2 to 8,2 to 9,2 to 10,2 to 11,2 to 12,2 to 13,2 to14 nucleotides of the oligonucleotide are modified nucleotides.Optionally, the oligonucleotides may have every nucleotide except 1, 2,3, 4, 5, 6, 7, 8, 9, or 10 nucleotides modified. Oligonucleotidemodifications are described further herein.

c. Modified Nucleosides

In some embodiments, the oligonucleotide described herein comprises atleast one nucleoside modified at the 2′ position of the sugar. In someembodiments, an oligonucleotide comprises at least one 2′-modifiednucleoside. In some embodiments, all of the nucleosides in theoligonucleotide are 2′-modified nucleosides.

In some embodiments, the oligonucleotide described herein comprises oneor more non-bicyclic 2′-modified nucleosides, e.g., 2′-deoxy, 2′-fluoro(2′-F), 2′-O-methyl (2′-O-Me), 2′-O-methoxyethyl (2′-MOE),2′-O-aminopropyl (2′-O-AP), 2′-O-dimethylaminoethyl (2′-O-DMAOE),2′-O-dimethylaminopropyl (2′-O-DMAP), 2′-O-dimethylaminoethyloxyethyl(2′-O-DMAEOE), or 2′-O—N-methylacetamido (2′-O-NMA) modified nucleoside.

In some embodiments, the oligonucleotide described herein comprises oneor more 2′-4′ bicyclic nucleosides in which the ribose ring comprises abridge moiety connecting two atoms in the ring, e.g., connecting the2′-O atom to the 4′-C atom via a methylene (LNA) bridge, an ethylene(ENA) bridge, or a (S)-constrained ethyl (cEt) bridge. Examples of LNAsare described in International Patent Application PublicationWO/2008/043753, published on Apr. 17, 2008, and entitled “RNA AntagonistCompounds For The Modulation Of PCSK9”, the contents of which areincorporated herein by reference in its entirety. Examples of ENAs areprovided in International Patent Publication No. WO 2005/042777,published on May 12, 2005, and entitled “APP/ENA Antisense”; Morita etal., Nucleic Acid Res., Suppl 1:241-242, 2001; Surono et al., Hum. GeneTher., 15:749-757, 2004; Koizumi, Curr. Opin. Mol. Ther., 8:144-149,2006 and Horie et al., Nucleic Acids Symp. Ser (Oxf), 49:171-172, 2005;the disclosures of which are incorporated herein by reference in theirentireties. Examples of cEt are provided in U.S. Pat. Nos. 7,101,993;7,399,845 and 7,569,686, each of which is herein incorporated byreference in its entirety.

In some embodiments, the oligonucleotide comprises a modified nucleosidedisclosed in one of the following United States Patent or PatentApplication Publications: U.S. Pat. No. 7,399,845, issued on Jul. 15,2008, and entitled “6-Modified Bicyclic Nucleic Acid Analogs”; U.S. Pat.No. 7,741,457, issued on Jun. 22, 2010, and entitled “6-ModifiedBicyclic Nucleic Acid Analogs”; U.S. Pat. No. 8,022,193, issued on Sep.20, 2011, and entitled “6-Modified Bicyclic Nucleic Acid Analogs”; U.S.Pat. No. 7,569,686, issued on Aug. 4, 2009, and entitled “Compounds AndMethods For Synthesis Of Bicyclic Nucleic Acid Analogs”; U.S. Pat. No.7,335,765, issued on Feb. 26, 2008, and entitled “Novel Nucleoside AndOligonucleotide Analogues”; U.S. Pat. No. 7,314,923, issued on Jan. 1,2008, and entitled “Novel Nucleoside And Oligonucleotide Analogues”;U.S. Pat. No. 7,816,333, issued on Oct. 19, 2010, and entitled“Oligonucleotide Analogues And Methods Utilizing The Same” and USPublication Number 2011/0009471 now U.S. Pat. No. 8,957,201, issued onFeb. 17, 2015, and entitled “Oligonucleotide Analogues And MethodsUtilizing The Same”, the entire contents of each of which areincorporated herein by reference for all purposes.

In some embodiments, the oligonucleotide comprises at least one modifiednucleoside that results in an increase in Tm of the oligonucleotide in arange of 1° C., 2° C., 3° C., 4° C., or 5° C. compared with anoligonucleotide that does not have the at least one modified nucleoside.The oligonucleotide may have a plurality of modified nucleosides thatresult in a total increase in Tm of the oligonucleotide in a range of 2°C., 3° C., 4° C., 5° C., 6° C., 7° C., 8° C., 9° C., 10° C., 15° C., 20°C., 25° C., 30° C., 35° C., 40° C., 45° C. or more compared with anoligonucleotide that does not have the modified nucleoside.

The oligonucleotide may comprise a mix of nucleosides of differentkinds. For example, an oligonucleotide may comprise a mix of2′-deoxyribonucleosides or ribonucleosides and 2′-fluoro modifiednucleosides. An oligonucleotide may comprise a mix ofdeoxyribonucleosides or ribonucleosides and 2′-O-Me modifiednucleosides. An oligonucleotide may comprise a mix of 2′-fluoro modifiednucleosides and 2′-O-Me modified nucleosides. An oligonucleotide maycomprise a mix of 2′-4′ bicyclic nucleosides and 2′-MOE, 2′-fluoro, or2′-O-Me modified nucleosides. An oligonucleotide may comprise a mix ofnon-bicyclic 2′-modified nucleosides (e.g., 2′-MOE, 2′-fluoro, or2′-O-Me) and 2′-4′ bicyclic nucleosides (e.g., LNA, ENA, cEt).

The oligonucleotide may comprise alternating nucleosides of differentkinds. For example, an oligonucleotide may comprise alternating2′-deoxyribonucleosides or ribonucleosides and 2′-fluoro modifiednucleosides. An oligonucleotide may comprise alternatingdeoxyribonucleosides or ribonucleosides and 2′-O-Me modifiednucleosides. An oligonucleotide may comprise alternating 2′-fluoromodified nucleosides and 2′-O-Me modified nucleosides. Anoligonucleotide may comprise alternating 2′-4′ bicyclic nucleosides and2′-MOE, 2′-fluoro, or 2′-O-Me modified nucleosides. An oligonucleotidemay comprise alternating non-bicyclic 2′-modified nucleosides (e.g.,2′-MOE, 2′-fluoro, or 2′-O-Me) and 2′-4′ bicyclic nucleosides (e.g.,LNA, ENA, cEt).

In some embodiments, an oligonucleotide described herein comprises a5′-vinylphosphonate modification, one or more abasic residues, and/orone or more inverted abasic residues.

d. Internucleoside Linkages/Backbones

In some embodiments, oligonucleotide may contain a phosphorothioate orother modified internucleoside linkage. In some embodiments, theoligonucleotide comprises phosphorothioate internucleoside linkages. Insome embodiments, the oligonucleotide comprises phosphorothioateinternucleoside linkages between at least two nucleotides. In someembodiments, the oligonucleotide comprises phosphorothioateinternucleoside linkages between all nucleotides. For example, in someembodiments, oligonucleotides comprise modified internucleoside linkagesat the first, second, and/or (e.g., and) third internucleoside linkageat the 5′ or 3′ end of the nucleotide sequence.

Phosphorus-containing linkages that may be used include, but are notlimited to, phosphorothioates, chiral phosphorothioates,phosphorodithioates, phosphotriesters, aminoalkylphosphotriesters,methyl and other alkyl phosphonates comprising 3′ alkylene phosphonatesand chiral phosphonates, phosphinates, phosphoramidates comprising3′-amino phosphoramidate and aminoalkylphosphoramidates,thionophosphoramidates, thionoalkylphosphonates,thionoalkylphosphotriesters, and boranophosphates having normal 3′-5′linkages, 2′-5′ linked analogs of these, and those having invertedpolarity wherein the adjacent pairs of nucleoside units are linked 3′-5′to 5′-3′ or 2′-5′ to 5′-2′; see U.S. Pat. Nos. 3,687,808; 4,469,863;4,476,301; 5,023,243; 5,177,196; 5,188,897; 5,264,423; 5,276,019;5,278,302; 5,286,717; 5,321,131; 5,399,676; 5,405,939; 5,453,496; 5,455,233; 5,466,677; 5,476,925; 5,519,126; 5,536,821; 5,541,306; 5,550,111;5,563, 253; 5,571,799; 5,587,361; and 5,625,050.

In some embodiments, oligonucleotides may have heteroatom backbones,such as methylene(methylimino) or MMI backbones; amide backbones (see DeMesmaeker et al. Ace. Chem. Res. 1995, 28:366-374); morpholino backbones(see Summerton and Weller, U.S. Pat. No. 5,034,506); or peptide nucleicacid (PNA) backbones (wherein the phosphodiester backbone of theoligonucleotide is replaced with a polyamide backbone, the nucleotidesbeing bound directly or indirectly to the aza nitrogen atoms of thepolyamide backbone, see Nielsen et al., Science 1991, 254, 1497).

e. Stereospecific Oligonucleotides

In some embodiments, internucleotidic phosphorus atoms ofoligonucleotides are chiral, and the properties of the oligonucleotidesare adjusted based on the configuration of the chiral phosphorus atoms.In some embodiments, appropriate methods may be used to synthesizeP-chiral oligonucleotide analogs in a stereocontrolled manner (e.g., asdescribed in Oka N, Wada T, Stereocontrolled synthesis ofoligonucleotide analogs containing chiral internucleotidic phosphorusatoms. Chem Soc Rev. 2011 December; 40(12):5829-43.) In someembodiments, phosphorothioate containing oligonucleotides are providedthat comprise nucleoside units that are joined together by eithersubstantially all Sp or substantially all Rp phosphorothioate intersugarlinkages. In some embodiments, such phosphorothioate oligonucleotideshaving substantially chirally pure intersugar linkages are prepared byenzymatic or chemical synthesis, as described, for example, in U.S. Pat.No. 5,587,261, issued on Dec. 12, 1996, the contents of which areincorporated herein by reference in their entirety. In some embodiments,chirally controlled oligonucleotides provide selective cleavage patternsof a target nucleic acid. For example, in some embodiments, a chirallycontrolled oligonucleotide provides single site cleavage within acomplementary sequence of a nucleic acid, as described, for example, inUS Patent Application Publication 20170037399 A1, published on Feb. 2,2017, entitled “CHIRAL DESIGN”, the contents of which are incorporatedherein by reference in their entirety.

f. Morpholinos

In some embodiments, the oligonucleotide may be a morpholino-basedcompounds. Morpholino-based oligomeric compounds are described in DwaineA. Braasch and David R. Corey, Biochemistry, 2002, 41(14), 4503-4510);Genesis, volume 30, issue 3, 2001; Heasman, J., Dev. Biol., 2002, 243,209-214; Nasevicius et al., Nat. Genet., 2000, 26, 216-220; Lacerra etal., Proc. Natl. Acad. Sci., 2000, 97, 9591-9596; and U.S. Pat. No.5,034,506, issued Jul. 23, 1991. In some embodiments, themorpholino-based oligomeric compound is a phosphorodiamidate morpholinooligomer (PMO) (e.g., as described in Iverson, Curr. Opin. Mol. Ther.,3:235-238, 2001; and Wang et al., J. Gene Med., 12:354-364, 2010; thedisclosures of which are incorporated herein by reference in theirentireties).

g. Peptide Nucleic Acids (PNAs)

In some embodiments, both a sugar and an internucleoside linkage (thebackbone) of the nucleotide units of an oligonucleotide are replacedwith novel groups. In some embodiments, the base units are maintainedfor hybridization with an appropriate nucleic acid target compound. Onesuch oligomeric compound, an oligonucleotide mimetic that has been shownto have excellent hybridization properties, is referred to as a peptidenucleic acid (PNA). In PNA compounds, the sugar-backbone of anoligonucleotide is replaced with an amide containing backbone, forexample, an aminoethylglycine backbone. The nucleobases are retained andare bound directly or indirectly to aza nitrogen atoms of the amideportion of the backbone. Representative publication that report thepreparation of PNA compounds include, but are not limited to, U.S. Pat.Nos. 5,539,082; 5,714,331; and 5,719,262, each of which is hereinincorporated by reference. Further teaching of PNA compounds can befound in Nielsen et al., Science, 1991, 254, 1497-1500.

h. Gapmers

In some embodiments, an oligonucleotide described herein is a gapmer. Agapmer oligonucleotide generally has the formula 5′-X—Y—Z-3′, with X andZ as flanking regions around a gap region Y. In some embodiments,flanking region X of formula 5′-X—Y—Z-3′ is also referred to as Xregion, flanking sequence X, 5′ wing region X, or 5′ wing segment. Insome embodiments, flanking region Z of formula 5′-X—Y—Z-3′ is alsoreferred to as Z region, flanking sequence Z, 3′ wing region Z, or 3′wing segment. In some embodiments, gap region Y of formula 5′-X—Y—Z-3′is also referred to as Y region, Y segment, or gap-segment Y. In someembodiments, each nucleoside in the gap region Y is a2′-deoxyribonucleoside, and neither the 5′ wing region X or the 3′ wingregion Z contains any 2′-deoxyribonucleosides.

In some embodiments, the Y region is a contiguous stretch ofnucleotides, e.g., a region of 6 or more DNA nucleotides, which arecapable of recruiting an RNAse, such as RNAse H. In some embodiments,the gapmer binds to the target nucleic acid, at which point an RNAse isrecruited and can then cleave the target nucleic acid. In someembodiments, the Y region is flanked both 5′ and 3′ by regions X and Zcomprising high-affinity modified nucleosides, e.g., one to sixhigh-affinity modified nucleosides. Examples of high affinity modifiednucleosides include, but are not limited to, 2′-modified nucleosides(e.g., 2′-MOE, 2′O-Me, 2′-F) or 2′-4′ bicyclic nucleosides (e.g., LNA,cEt, ENA). In some embodiments, the flanking sequences X and Z may be of1-20 nucleotides, 1-8 nucleotides, or 1-5 nucleotides in length. Theflanking sequences X and Z may be of similar length or of dissimilarlengths. In some embodiments, the gap-segment Y may be a nucleotidesequence of 5-20 nucleotides, 5-15 twelve nucleotides, or 6-10nucleotides in length.

In some embodiments, the gap region of the gapmer oligonucleotides maycontain modified nucleotides known to be acceptable for efficient RNaseH action in addition to DNA nucleotides, such as C4′-substitutednucleotides, acyclic nucleotides, and arabino-configured nucleotides. Insome embodiments, the gap region comprises one or more unmodifiedinternucleoside linkages. In some embodiments, one or both flankingregions each independently comprise one or more phosphorothioateinternucleoside linkages (e.g., phosphorothioate internucleosidelinkages or other linkages) between at least two, at least three, atleast four, at least five or more nucleotides. In some embodiments, thegap region and two flanking regions each independently comprise modifiedinternucleoside linkages (e.g., phosphorothioate internucleosidelinkages or other linkages) between at least two, at least three, atleast four, at least five or more nucleotides.

A gapmer may be produced using appropriate methods. Representative U.S.patents, U.S. patent publications, and PCT publications that teach thepreparation of gapmers include, but are not limited to, U.S. Pat. Nos.5,013,830; 5,149,797; 5,220,007; 5,256,775; 5,366,878; 5,403,711;5,491,133; 5,565,350; 5,623,065; 5,652,355; 5,652,356; 5,700,922;5,898,031; 7,015,315; 7,101,993; 7,399,845; 7,432,250; 7,569,686;7,683,036; 7,750,131; 8,580,756; 9,045,754; 9,428,534; 9,695,418;10,017,764; 10,260,069; 9,428,534; 8,580,756; U.S. patent publicationNos. US20050074801, US20090221685; US20090286969, US20100197762, andUS20110112170; PCT publication Nos. WO2004069991; WO2005023825;WO2008049085 and WO2009090182; and EP Patent No. EP2,149,605, each ofwhich is herein incorporated by reference in its entirety.

In some embodiments, a gapmer is 10-40 nucleosides in length. Forexample, a gapmer may be 10-40, 10-35, 10-30, 10-25, 10-20, 10-15,15-40, 15-35, 15-30, 15-25, 15-20, 20-40, 20-35, 20-30, 20-25, 25-40,25-35, 25-30, 30-40, 30-35, or 35-40 nucleosides in length. In someembodiments, a gapmer is 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21,22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39,or 40 nucleosides in length.

In some embodiments, the gap region Y in a gapmer is 5-20 nucleosides inlength. For example, the gap region Y may be 5-20, 5-15, 5-10, 10-20,10-15, or 15-20 nucleosides in length. In some embodiments, the gapregion Y is 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20nucleosides in length. In some embodiments, each nucleoside in the gapregion Y is a 2′-deoxyribonucleoside. In some embodiments, allnucleosides in the gap region Y are 2′-deoxyribonucleosides. In someembodiments, one or more of the nucleosides in the gap region Y is amodified nucleoside (e.g., a 2′ modified nucleoside such as thosedescribed herein). In some embodiments, one or more cytosines in the gapregion Y are optionally 5-methyl-cytosines. In some embodiments, eachcytosine in the gap region Y is a 5-methyl-cytosines.

In some embodiments, the 5′ wing region of a gapmer (X in the5′-X—Y—Z-3′ formula) and the 3′ wing region of a gapmer (Z in the5′-X—Y—Z-3′ formula) are independently 1-20 nucleosides long. Forexample, the 5′ wing region of a gapmer (X in the 5′-X—Y—Z-3′ formula)and the 3′ wing region of the gapmer (Z in the 5′-X—Y—Z-3′ formula) maybe independently 1-20, 1-15, 1-10, 1-7, 1-5, 1-3, 1-2, 2-5, 2-7, 3-5,3-7, 5-20, 5-15, 5-10, 10-20, 10-15, or 15-20 nucleosides long. In someembodiments, the 5′ wing region of the gapmer (X in the 5′-X—Y—Z-3′formula) and the 3′ wing region of the gapmer (Z in the 5′-X—Y—Z-3′formula) are independently 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,14, 15, 16, 17, 18, 19, or 20 nucleosides long. In some embodiments, the5′ wing region of the gapmer (X in the 5′-X—Y—Z-3′ formula) and the 3′wing region of the gapmer (Z in the 5′-X—Y—Z-3′ formula) are of the samelength. In some embodiments, the 5′ wing region of the gapmer (X in the5′-X—Y—Z-3′ formula) and the 3′ wing region of the gapmer (Z in the5′-X—Y—Z-3′ formula) are of different lengths. In some embodiments, the5′ wing region of the gapmer (X in the 5′-X—Y—Z-3′ formula) is longerthan the 3′ wing region of the gapmer (Z in the 5′-X—Y—Z-3′ formula). Insome embodiments, the 5′ wing region of the gapmer (X in the 5′-X—Y—Z-3′formula) is shorter than the 3′ wing region of the gapmer (Z in the5′-X—Y—Z-3′ formula).

In some embodiments, a gapmer comprises a 5′-X—Y—Z-3′ of 5-10-5, 4-12-4,3-14-3, 2-16-2, 1-18-1, 3-10-3, 2-10-2, 1-10-1, 2-8-2, 4-6-4, 3-6-3,2-6-2, 4-7-4, 3-7-3, 2-7-2, 4-8-4, 3-8-3, 2-8-2, 1-8-1, 2-9-2, 1-9-1,2-10-2, 1-10-1, 1-12-1, 1-16-1, 2-15-1, 1-15-2, 1-14-3, 3-14-1, 2-14-2,1-13-4, 4-13-1, 2-13-3, 3-13-2, 1-12-5, 5-12-1, 2-12-4, 4-12-2, 3-12-3,1-11-6, 6- 11-1, 2-11-5, 5-11-2, 3-11-4, 4-11-3, 1-17-1, 2-16-1, 1-16-2,1-15-3, 3-15-1, 2-15-2, 1-14-4, 4-14-1, 2-14-3, 3-14-2, 1-13-5, 5-13-1,2-13-4, 4-13-2, 3-13-3, 1-12-6, 6-12-1, 2-12-5, 5-12-2, 3-12-4, 4-12-3,1-11-7, 7-11-1, 2-11-6, 6-11-2, 3-11-5, 5-11-3, 4-11-4, 1-18-1, 1-17-2,2-17-1, 1-16-3, 1-16-3, 2-16-2, 1-15-4, 4-15-1, 2-15-3, 3-15-2, 1-14-5,5-14-1, 2-14-4, 4-14-2, 3-14-3, 1-13-6, 6-13-1, 2-13-5, 5-13-2, 3-13-4,4-13-3, 1-12-7, 7-12-1, 2-12-6, 6-12-2, 3-12-5, 5-12-3, 1-11-8, 8-11-1,2-11-7, 7-11-2, 3-11-6, 6-11-3, 4-11-5, 5-11-4, 1-18-1, 1-17-2, 2-17-1,1-16-3, 3-16-1, 2-16-2, 1-15-4, 4-15-1, 2-15-3, 3-15-2, 1-14-5, 2-14-4,4-14-2, 3-14-3, 1-13-6, 6-13-1, 2-13-5, 5-13-2, 3-13-4, 4-13-3, 1-12-7,7-12-1, 2-12-6, 6-12-2, 3-12-5, 5-12-3, 1-11-8, 8-11-1, 2-11-7, 7-11-2,3-11-6, 6-11-3, 4-11-5, 5-11-4, 1-19-1, 1-18-2, 2-18-1, 1-17-3, 3-17-1,2-17-2, 1-16-4, 4-16-1, 2-16-3, 3-16-2, 1-15-5, 2-15-4, 4-15-2, 3-15-3,1-14-6, 6-14-1, 2-14-5, 5-14-2, 3-14-4, 4-14-3, 1-13-7, 7-13-1, 2-13-6,6-13-2, 3-13-5, 5-13-3, 4-13-4, 1-12-8, 8-12-1, 2-12-7, 7-12-2, 3-12-6,6-12-3, 4-12-5, 5-12-4, 2-11-8, 8-11-2, 3-11-7, 7-11-3, 4-11-6, 6-11-4,5-11-5, 1-20-1, 1-19-2, 2-19-1, 1-18-3, 3-18-1, 2-18-2, 1-17-4, 4-17-1,2-17-3, 3-17-2, 1-16-5, 2-16-4, 4-16-2, 3-16-3, 1-15-6, 6-15-1, 2-15-5,5-15-2, 3-15-4, 4-15-3, 1-14-7, 7-14-1, 2-14-6, 6-14-2, 3-14-5, 5-14-3,4-14-4, 1-13-8, 8-13-1, 2-13-7, 7-13-2, 3-13-6, 6-13-3, 4-13-5, 5-13-4,2-12-8, 8-12-2, 3-12-7, 7-12-3, 4-12-6, 6-12-4, 5-12-5, 3-11-8, 8-11-3,4-11-7, 7-11-4, 5-11-6, 6-11-5, 1-21-1, 1-20-2, 2-20-1, 1-20-3, 3-19-1,2-19-2, 1-18-4, 4-18-1, 2-18-3, 3-18-2, 1-17-5, 2-17-4, 4-17-2, 3-17-3,1-16-6, 6-16-1, 2-16-5, 5-16-2, 3-16-4, 4-16-3, 1-15-7, 7-15-1, 2-15-6,6-15-2, 3-15-5, 5-15-3, 4-15-4, 1-14-8, 8-14-1, 2-14-7, 7-14-2, 3-14-6,6-14-3, 4-14-5, 5-14-4, 2-13-8, 8-13-2, 3-13-7, 7-13-3, 4-13-6, 6-13-4,5-13-5, 1-12-10, 10-12-1, 2-12-9, 9-12-2, 3-12-8, 8-12-3, 4-12-7,7-12-4, 5-12-6, 6-12-5, 4-11-8, 8-11-4, 5-11-7, 7-11-5, 6-11-6, 1-22-1,1-21-2, 2-21-1, 1-21-3, 3-20-1, 2-20-2, 1-19-4, 4-19-1, 2-19-3, 3-19-2,1-18-5, 2-18-4, 4-18-2, 3-18-3, 1-17-6, 6-17-1, 2-17-5, 5-17-2, 3-17-4,4-17-3, 1-16-7, 7-16-1, 2-16-6, 6-16-2, 3-16-5, 5-16-3, 4-16-4, 1-15-8,8-15-1, 2-15-7, 7-15-2, 3-15-6, 6-15-3, 4-15-5, 5-15-4, 2-14-8, 8-14-2,3-14-7, 7-14-3, 4-14-6, 6-14-4, 5-14-5, 3-13-8, 8-13-3, 4-13-7, 7-13-4,5-13-6, 6-13-5, 4-12-8, 8-12-4, 5-12-7, 7-12-5, 6-12-6, 5-11-8, 8-11-5,6-11-7, or 7-11-6. The numbers indicate the number of nucleosides in X,Y, and Z regions in the 5′-X—Y—Z-3′ gapmer.

In some embodiments, one or more nucleosides in the 5′ wing region of agapmer (X in the 5′-X—Y—Z-3′ formula) or the 3′ wing region of a gapmer(Z in the 5′-X—Y—Z-3′ formula) are modified nucleotides (e.g.,high-affinity modified nucleosides). In some embodiments, the modifiednucleoside (e.g., high-affinity modified nucleosides) is a 2′-modifiednucleoside. In some embodiments, the 2′-modified nucleoside is a 2′-4′bicyclic nucleoside or a non-bicyclic 2′-modified nucleoside. In someembodiments, the high-affinity modified nucleoside is a 2′-4′ bicyclicnucleoside (e.g., LNA, cEt, or ENA) or a non-bicyclic 2′-modifiednucleoside (e.g., 2′-fluoro (2′-F), 2′-O-methyl (2′-O-Me),2′-O-methoxyethyl (2′-MOE), 2′-O-aminopropyl (2′-O-AP),2′-O-dimethylaminoethyl (2′-O-DMA0E), 2′-O-dimethylaminopropyl(2′-O-DMAP), 2′-O-dimethylaminoethyloxyethyl (2′-O-DMAEOE), or2′-O—N-methylacetamido (2′-O-NMA)).

In some embodiments, one or more nucleosides in the 5′ wing region of agapmer (X in the 5′-X—Y—Z-3′ formula) are high-affinity modifiednucleosides. In some embodiments, each nucleoside in the 5′ wing regionof the gapmer (X in the 5′-X—Y—Z-3′ formula) is a high-affinity modifiednucleoside. In some embodiments, one or more nucleosides in the 3′ wingregion of a gapmer (Z in the 5′-X—Y—Z-3′ formula) are high-affinitymodified nucleosides. In some embodiments, each nucleoside in the 3′wing region of the gapmer (Z in the 5′-X—Y—Z-3′ formula) is ahigh-affinity modified nucleoside. In some embodiments, one or morenucleosides in the 5′ wing region of the gapmer (X in the 5′-X—Y—Z-3′formula) are high-affinity modified nucleosides and one or morenucleosides in the 3′ wing region of the gapmer (Z in the 5′-X—Y—Z-3′formula) are high-affinity modified nucleosides. In some embodiments,each nucleoside in the 5′ wing region of the gapmer (X in the5′-X—Y—Z-3′ formula) is a high-affinity modified nucleoside and eachnucleoside in the 3′ wing region of the gapmer (Z in the 5′-X—Y—Z-3′formula) is high-affinity modified nucleoside.

In some embodiments, the 5′ wing region of a gapmer (X in the5′-X—Y—Z-3′ formula) comprises the same high affinity nucleosides as the3′ wing region of the gapmer (Z in the 5′-X—Y—Z-3′ formula). Forexample, the 5′ wing region of the gapmer (X in the 5′-X—Y—Z-3′ formula)and the 3′ wing region of the gapmer (Z in the 5′-X—Y—Z-3′ formula) maycomprise one or more non-bicyclic 2′-modified nucleosides (e.g., 2′-MOEor 2′-O-Me). In another example, the 5′ wing region of the gapmer (X inthe 5′-X—Y—Z-3′ formula) and the 3′ wing region of the gapmer (Z in the5′-X—Y—Z-3′ formula) may comprise one or more 2′-4′ bicyclic nucleosides(e.g., LNA or cEt). In some embodiments, each nucleoside in the 5′ wingregion of the gapmer (X in the 5′-X—Y—Z-3′ formula) and the 3′ wingregion of the gapmer (Z in the 5′-X—Y—Z-3′ formula) is a non-bicyclic2′-modified nucleosides (e.g., 2′-MOE or 2′-O-Me). In some embodiments,each nucleoside in the 5′ wing region of the gapmer (X in the5′-X—Y—Z-3′ formula) and the 3′ wing region of the gapmer (Z in the5′-X—Y—Z-3′ formula) is a 2′-4′ bicyclic nucleosides (e.g., LNA or cEt).

In some embodiments, a gapmer comprises a 5′-X—Y—Z-3′ configuration,wherein X and Z is independently 1-7 (e.g., 1, 2, 3, 4, 5, 6, or 7)nucleosides in length and Y is 6-10 (e.g., 6, 7, 8, 9, or 10)nucleosides in length, wherein each nucleoside in X and Z is anon-bicyclic 2′-modified nucleosides (e.g., 2′-MOE or 2′-O-Me) and eachnucleoside in Y is a 2′-deoxyribonucleoside. In some embodiments, thegapmer comprises a 5′-X—Y—Z-3′ configuration, wherein X and Z isindependently 1-7 (e.g., 1, 2, 3, 4, 5, 6, or 7) nucleosides in lengthand Y is 6-10 (e.g., 6, 7, 8, 9, or 10) nucleosides in length, whereineach nucleoside in X and Z is a 2′-4′ bicyclic nucleosides (e.g., LNA orcEt) and each nucleoside in Y is a 2′-deoxyribonucleoside. In someembodiments, the 5′ wing region of the gapmer (X in the 5′-X—Y—Z-3′formula) comprises different high affinity nucleosides as the 3′ wingregion of the gapmer (Z in the 5′-X—Y—Z-3′ formula). For example, the 5′wing region of the gapmer (X in the 5′-X—Y—Z-3′ formula) may compriseone or more non-bicyclic 2′-modified nucleosides (e.g., 2′-MOE or2′-O-Me) and the 3′ wing region of the gapmer (Z in the 5′-X—Y—Z-3′formula) may comprise one or more 2′-4′ bicyclic nucleosides (e.g., LNAor cEt). In another example, the 3′ wing region of the gapmer (Z in the5′-X—Y—Z-3′ formula) may comprise one or more non-bicyclic 2′-modifiednucleosides (e.g., 2′-MOE or 2′-O-Me) and the 5′ wing region of thegapmer (X in the 5′-X—Y—Z-3′ formula) may comprise one or more 2′-4′bicyclic nucleosides (e.g., LNA or cEt).

In some embodiments, a gapmer comprises a 5′-X—Y—Z-3′ configuration,wherein X and Z is independently 1-7 (e.g., 1, 2, 3, 4, 5, 6, or 7)nucleosides in length and Y is 6-10 (e.g., 6, 7, 8, 9, or 10)nucleosides in length, wherein each nucleoside in X is a non-bicyclic2′-modified nucleosides (e.g., 2′-MOE or 2′-O-Me), each nucleoside in Zis a 2′-4′ bicyclic nucleosides (e.g., LNA or cEt), and each nucleosidein Y is a 2′-deoxyribonucleoside. In some embodiments, the gapmercomprises a 5′-X—Y—Z-3′ configuration, wherein X and Z is independently1-7 (e.g., 1, 2, 3, 4, 5, 6, or 7) nucleosides in length and Y is 6-10(e.g., 6, 7, 8, 9, or 10) nucleosides in length, wherein each nucleosidein X is a 2′-4′ bicyclic nucleosides (e.g., LNA or cEt), each nucleosidein Z is a non-bicyclic 2′-modified nucleosides (e.g., 2′-MOE or 2′-O-Me)and each nucleoside in Y is a 2′-deoxyribonucleoside.

In some embodiments, the 5′ wing region of a gapmer (X in the5′-X—Y—Z-3′ formula) comprises one or more non-bicyclic 2′-modifiednucleosides (e.g., 2′-MOE or 2′-O-Me) and one or more 2′-4′ bicyclicnucleosides (e.g., LNA or cEt). In some embodiments, the 3′ wing regionof the gapmer (Z in the 5′-X—Y—Z-3′ formula) comprises one or morenon-bicyclic 2′-modified nucleosides (e.g., 2′-MOE or 2′-O-Me) and oneor more 2′-4′ bicyclic nucleosides (e.g., LNA or cEt). In someembodiments, both the 5′ wing region of the gapmer (X in the 5′-X—Y—Z-3′formula) and the 3′ wing region of the gapmer (Z in the 5′-X—Y—Z-3′formula) comprise one or more non-bicyclic 2′-modified nucleosides(e.g., 2′-MOE or 2′-O-Me) and one or more 2′-4′ bicyclic nucleosides(e.g., LNA or cEt).

In some embodiments, a gapmer comprises a 5′-X—Y—Z-3′ configuration,wherein X and Z is independently 2-7 (e.g., 2, 3, 4, 5, 6, or 7)nucleosides in length and Y is 6-10 (e.g., 6, 7, 8, 9, or 10)nucleosides in length, wherein at least one but not all (e.g., 1, 2, 3,4, 5, or 6) of positions 1, 2, 3, 4, 5, 6, or 7 in X (the 5′ mostposition is position 1) is a non-bicyclic 2′-modified nucleoside (e.g.,2′-MOE or 2′-O-Me), wherein the rest of the nucleosides in both X and Zare 2′-4′ bicyclic nucleosides (e.g., LNA or cEt), and wherein eachnucleoside in Y is a 2′deoxyribonucleoside. In some embodiments, thegapmer comprises a 5′-X—Y—Z-3′ configuration, wherein X and Z isindependently 2-7 (e.g., 2, 3, 4, 5, 6, or 7) nucleosides in length andY is 6-10 (e.g., 6, 7, 8, 9, or 10) nucleosides in length, wherein atleast one but not all (e.g., 1, 2, 3, 4, 5, or 6) of positions 1, 2, 3,4, 5, 6, or 7 in Z (the 5′ most position is position 1) is anon-bicyclic 2′-modified nucleoside (e.g., 2′-MOE or 2′-O-Me), whereinthe rest of the nucleosides in both X and Z are 2′-4′ bicyclicnucleosides (e.g., LNA or cEt), and wherein each nucleoside in Y is a2′deoxyribonucleoside. In some embodiments, the gapmer comprises a5′-X—Y—Z-3′ configuration, wherein X and Z is independently 2-7 (e.g.,2, 3, 4, 5, 6, or 7) nucleosides in length and Y is 6-10 (e.g., 6, 7, 8,9, or 10) nucleosides in length, wherein at least one but not all (e.g.,1, 2, 3, 4, 5, or 6) of positions 1, 2, 3, 4, 5, 6, or 7 in X and atleast one of positions but not all (e.g., 1, 2, 3, 4, 5, or 6) 1, 2, 3,4, 5, 6, or 7 in Z (the 5′ most position is position 1) is anon-bicyclic 2′-modified nucleoside (e.g., 2′-MOE or 2′-O-Me), whereinthe rest of the nucleosides in both X and Z are 2′-4′ bicyclicnucleosides (e.g., LNA or cEt), and wherein each nucleoside in Y is a2′deoxyribonucleoside.

Non-limiting examples of gapmers configurations with a mix ofnon-bicyclic 2′-modified nucleoside (e.g., 2′-MOE or 2′-O-Me) and 2′-4′bicyclic nucleosides (e.g., LNA or cEt) in the 5′ wing region of thegapmer (X in the 5′-X—Y—Z-3′ formula) and/or the 3′ wing region of thegapmer (Z in the 5′-X—Y—Z-3′ formula) include: BBB-(D)n-BBBAA;KKK-(D)n-KKKAA; LLL-(D)n-LLLAA; BBB-(D)n-BBBEE; KKK-(D)n-KKKEE;LLL-(D)n-LLLEE; BBB-(D)n-BBBAA; KKK-(D)n-KKKAA; LLL-(D)n-LLLAA;BBB-(D)n-BBBEE; KKK-(D)n-KKKEE; LLL-(D)n-LLLEE; BBB-(D)n-BBBAAA;KKK-(D)n-KKKAAA; LLL-(D)n-LLLAAA; BBB-(D)n-BBBEEE; KKK-(D)n-KKKEEE;LLL-(D)n-LLLEEE; BBB-(D)n-BBBAAA; KKK-(D)n-KKKAAA; LLL-(D)n-LLLAAA;BBB-(D)n-BBBEEE; KKK-(D)n-KKKEEE; LLL-(D)n-LLLEEE; BABA-(D)n-ABAB;KAKA-(D)n-AKAK; LALA-(D)n-ALAL; BEBE-(D)n-EBEB; KEKE-(D)n-EKEK;LELE-(D)n-ELEL; BABA-(D)n-ABAB; KAKA-(D)n-AKAK; LALA-(D)n-ALAL;BEBE-(D)n-EBEB; KEKE-(D)n-EKEK; LELE-(D)n-ELEL; ABAB-(D)n-ABAB;AKAK-(D)n-AKAK; ALAL-(D)n-ALAL; EBEB-(D)n-EBEB; EKEK-(D)n-EKEK;ELEL-(D)n-ELEL; ABAB-(D)n-ABAB; AKAK-(D)n-AKAK; ALAL-(D)n-ALAL;EBEB-(D)n-EBEB; EKEK-(D)n-EKEK; ELEL-(D)n-ELEL; AABB-(D)n-BBAA;BBAA-(D)n-AABB; AAKK-(D)n-KKAA; AALL-(D)n-LLAA; EEBB-(D)n-BBEE;EEKK-(D)n-KKEE; EELL-(D)n-LLEE; AABB-(D)n-BBAA; AAKK-(D)n-KKAA;AALL-(D)n-LLAA; EEBB-(D)n-BBEE; EEKK-(D)n-KKEE; EELL-(D)n-LLEE;BBB-(D)n-BBA; KKK-(D)n-KKA; LLL-(D)n-LLA; BBB-(D)n-BBE; KKK-(D)n-KKE;LLL-(D)n-LLE; BBB-(D)n-BBA; KKK-(D)n-KKA; LLL-(D)n-LLA; BBB-(D)n-BBE;KKK-(D)n-KKE; LLL-(D)n-LLE; BBB-(D)n-BBA; KKK-(D)n-KKA; LLL-(D)n-LLA;BBB-(D)n-BBE; KKK-(D)n-KKE; LLL-(D)n-LLE; ABBB-(D)n-BBBA;AKKK-(D)n-KKKA; ALLL-(D)n-LLLA; EBBB-(D)n-BBBE; EKKK-(D)n-KKKE;ELLL-(D)n-LLLE; ABBB-(D)n-BBBA; AKKK-(D)n-KKKA; ALLL-(D)n-LLLA;EBBB-(D)n-BBBE; EKKK-(D)n-KKKE; ELLL-(D)n-LLLE; ABBB-(D)n-BBBAA;AKKK-(D)n-KKKAA; ALLL-(D)n-LLLAA; EBBB-(D)n-BBBEE; EKKK-(D)n-KKKEE;ELLL-(D)n-LLLEE; ABBB-(D)n-BBBAA; AKKK-(D)n-KKKAA; ALLL-(D)n-LLLAA;EBBB-(D)n-BBBEE; EKKK-(D)n-KKKEE; ELLL-(D)n-LLLEE; AABBB-(D)n-BBB;AAKKK-(D)n-KKK; AALLL-(D)n-LLL; EEBBB-(D)n-BBB; EEKKK-(D)n-KKK;EELLL-(D)n-LLL; AABBB-(D)n-BBB; AAKKK-(D)n-KKK; AALLL-(D)n-LLL;EEBBB-(D)n-BBB; EEKKK-(D)n-KKK; EELLL-(D)n-LLL; AABBB-(D)n-BBBA;AAKKK-(D)n-KKKA; AALLL-(D)n-LLLA; EEBBB-(D)n-BBBE; EEKKK-(D)n-KKKE;EELLL-(D)n-LLLE; AABBB-(D)n-BBBA; AAKKK-(D)n-KKKA; AALLL-(D)n-LLLA;EEBBB-(D)n-BBBE; EEKKK-(D)n-KKKE; EELLL-(D)n-LLLE; ABBAABB-(D)n-BB;AKKAAKK-(D)n-KK; ALLAALLL-(D)n-LL; EBBEEBB-(D)n-BB; EKKEEKK-(D)n-KK;ELLEELL-(D)n-LL; ABBAABB-(D)n-BB; AKKAAKK-(D)n-KK; ALLAALL-(D)n-LL;EBBEEBB-(D)n-BB; EKKEEKK-(D)n-KK; ELLEELL-(D)n-LL; ABBABB-(D)n-BBB;AKKAKK-(D)n-KKK; ALLALLL-(D)n-LLL; EBBEBB-(D)n-BBB; EKKEKK-(D)n-KKK;ELLELL-(D)n-LLL; ABBABB-(D)n-BBB; AKKAKK-(D)n-KKK; ALLALL-(D)n-LLL;EBBEBB-(D)n-BBB; EKKEKK-(D)n-KKK; ELLELL-(D)n-LLL; EEEK-(D)n-EEEEEEEE;EEK-(D)n-EEEEEEEEE; EK-(D)n-EEEEEEEEEE; EK-(D)n-EEEKK; K-(D)n-EEEKEKE;K-(D)n-EEEKEKEE; K-(D)n-EEKEK; EK-(D)n-EEEEKEKE; EK-(D)n-EEEKEK;EEK-(D)n-KEEKE; EK-(D)n-EEKEK; EK-(D)n-KEEK; EEK-(D)n-EEEKEK;EK-(D)n-KEEEKEE; EK-(D)n-EEKEKE; EK-(D)n-EEEKEKE; and EK-(D)n-EEEEKEK.“A” nucleosides comprise a 2′-modified nucleoside; “B” represents a2′-4′ bicyclic nucleoside; “K” represents a constrained ethyl nucleoside(cEt); “L” represents an LNA nucleoside; and “E” represents a 2′-MOEmodified ribonucleoside; “D” represents a 2′-deoxyribonucleoside; “n”represents the length of the gap segment (Y in the 5′-X—Y—Z-3′configuration) and is an integer between 1-20.

In some embodiments, any one of the gapmers described herein comprisesone or more modified nucleoside linkages (e.g., a phosphorothioatelinkage) in each of the X, Y, and Z regions. In some embodiments, eachinternucleoside linkage in the any one of the gapmers described hereinis a phosphorothioate linkage. In some embodiments, each of the X, Y,and Z regions independently comprises a mix of phosphorothioate linkagesand phosphodiester linkages. In some embodiments, each internucleosidelinkage in the gap region Y is a phosphorothioate linkage, the 5′ wingregion X comprises a mix of phosphorothioate linkages and phosphodiesterlinkages, and the 3′ wing region Z comprises a mix of phosphorothioatelinkages and phosphodiester linkages.

i. Mixmers

In some embodiments, an oligonucleotide described herein may be a mixmeror comprise a mixmer sequence pattern. In general, mixmers areoligonucleotides that comprise both naturally and non-naturallyoccurring nucleosides or comprise two different types of non-naturallyoccurring nucleosides typically in an alternating pattern. Mixmersgenerally have higher binding affinity than unmodified oligonucleotidesand may be used to specifically bind a target molecule, e.g., to block abinding site on the target molecule. Generally, mixmers do not recruitan RNase to the target molecule and thus do not promote cleavage of thetarget molecule. Such oligonucleotides that are incapable of recruitingRNase H have been described, for example, see WO2007/112754 orWO2007/112753.

In some embodiments, the mixmer comprises or consists of a repeatingpattern of nucleoside analogues and naturally occurring nucleosides, orone type of nucleoside analogue and a second type of nucleosideanalogue. However, a mixmer need not comprise a repeating pattern andmay instead comprise any arrangement of modified nucleosides andnaturally occurring nucleoside s or any arrangement of one type ofmodified nucleoside and a second type of modified nucleoside. Therepeating pattern, may, for instance be every second or every thirdnucleoside is a modified nucleoside, such as LNA, and the remainingnucleosides are naturally occurring nucleosides, such as DNA, or are a2′ substituted nucleoside analogue such as 2′-MOE or 2′ fluoroanalogues, or any other modified nucleoside described herein. It isrecognized that the repeating pattern of modified nucleoside, such asLNA units, may be combined with modified nucleoside at fixedpositions—e.g. at the 5′ or 3′ termini.

In some embodiments, a mixmer does not comprise a region of more than 5,more than 4, more than 3, or more than 2 consecutive naturally occurringnucleosides, such as DNA nucleosides. In some embodiments, the mixmercomprises at least a region consisting of at least two consecutivemodified nucleosides, such as at least two consecutive LNAs. In someembodiments, the mixmer comprises at least a region consisting of atleast three consecutive modified nucleoside units, such as at leastthree consecutive LNAs.

In some embodiments, the mixmer does not comprise a region of more than7, more than 6, more than 5, more than 4, more than 3, or more than 2consecutive nucleoside analogues, such as LNAs. In some embodiments, LNAunits may be replaced with other nucleoside analogues, such as thosereferred to herein.

Mixmers may be designed to comprise a mixture of affinity enhancingmodified nucleosides, such as in non-limiting example LNA nucleosidesand 2′-O-Me nucleosides. In some embodiments, a mixmer comprisesmodified internucleoside linkages (e.g., phosphorothioateinternucleoside linkages or other linkages) between at least two, atleast three, at least four, at least five or more nucleosides.

A mixmer may be produced using any suitable method. Representative U.S.patents, U.S. patent publications, and PCT publications that teach thepreparation of mixmers include U.S. patent publication Nos.US20060128646, US20090209748, US20090298916, US20110077288, andUS20120322851, and U.S. Pat. No. 7,687,617.

In some embodiments, a mixmer comprises one or more morpholinonucleosides. For example, in some embodiments, a mixmer may comprisemorpholino nucleosides mixed (e.g., in an alternating manner) with oneor more other nucleosides (e.g., DNA, RNA nucleosides) or modifiednucleosides (e.g., LNA, 2′-O-Me nucleosides).

In some embodiments, mixmers are useful for splice correcting or exonskipping, for example, as reported in Touznik A., et al., LNA/DNAmixmer-based antisense oligonucleotides correct alternative splicing ofthe SMN2 gene and restore SMN protein expression in type 1 SMAfibroblasts Scientific Reports, volume 7, Article number: 3672 (2017),Chen S. et al., Synthesis of a Morpholino Nucleic Acid (MNA)-UridinePhosphoramidite, and Exon Skipping Using MNA/2′-O-Methyl MixmerAntisense Oligonucleotide, Molecules 2016, 21, 1582, the contents ofeach which are incorporated herein by reference.

j. RNA Interference (RNAi)

In some embodiments, oligonucleotides provided herein may be in the formof small interfering RNAs (siRNA), also known as short interfering RNAor silencing RNA. SiRNA, is a class of double-stranded RNA molecules,typically about 20-25 base pairs in length that target nucleic acids(e.g., mRNAs) for degradation via the RNA interference (RNAi) pathway incells. Specificity of siRNA molecules may be determined by the bindingof the antisense strand of the molecule to its target RNA. EffectivesiRNA molecules are generally less than 30 to 35 base pairs in length toprevent the triggering of non-specific RNA interference pathways in thecell via the interferon response, although longer siRNA can also beeffective. In some embodiments, the siRNA molecules are 7, 8, 9, 10, 11,12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29,30, 35, 40, 45, 50, or more base pairs in length. In some embodiments,the siRNA molecules are 8 to 30 base pairs in length, 10 to 15 basepairs in length, 10 to 20 base pairs in length, 15 to 25 base pairs inlength, 19 to 21 base pairs in length, 21 to 23 base pairs in length.

Following selection of an appropriate target RNA sequence, siRNAmolecules that comprise a nucleotide sequence complementary to all or aportion of the target sequence, i.e. an antisense sequence, can bedesigned and prepared using appropriate methods (see, e.g., PCTPublication Number WO 2004/016735; and U.S. Patent Publication Nos.2004/0077574 and 2008/0081791). The siRNA molecule can be doublestranded (i.e. a dsRNA molecule comprising an antisense strand and acomplementary sense strand strand that hybridizes to form the dsRNA) orsingle-stranded (i.e. a ssRNA molecule comprising just an antisensestrand). The siRNA molecules can comprise a duplex, asymmetric duplex,hairpin or asymmetric hairpin secondary structure, havingself-complementary sense and antisense strands.

In some embodiments, the antisense strand of the siRNA molecule is 7, 8,9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26,27, 28, 29, 30, 35, 40, 45, 50, or more nucleotides in length. In someembodiments, the antisense strand is 8 to 50 nucleotides in length, 8 to40 nucleotides in length, 8 to 30 nucleotides in length, 10 to 15nucleotides in length, 10 to 20 nucleotides in length, 15 to 25nucleotides in length, 19 to 21 nucleotides in length, 21 to 23nucleotides in lengths.

In some embodiments, the sense strand of the siRNA molecule is 7, 8, 9,10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27,28, 29, 30, 35, 40, 45, 50, or more nucleotides in length. In someembodiments, the sense strand is 8 to 50 nucleotides in length, 8 to 40nucleotides in length, 8 to 30 nucleotides in length, 10 to 15nucleotides in length, 10 to 20 nucleotides in length, 15 to 25nucleotides in length, 19 to 21 nucleotides in length, 21 to 23nucleotides in lengths.

In some embodiments, siRNA molecules comprise an antisense strandcomprising a region of complementarity to a target region in a targetmRNA. In some embodiments, the region of complementarity is at least80%, at least 85%, at least 90%, at least 91%, at least 92%, at least93%, at least 94%, at least 95%, at least 96%, at least 97%, at least98%, at least 99% or 100% complementary to a target region in a targetmRNA. In some embodiments, the target region is a region of consecutivenucleotides in the target mRNA. In some embodiments, a complementarynucleotide sequence need not be 100% complementary to that of its targetto be specifically hybridizable or specific for a target RNA sequence.

In some embodiments, siRNA molecules comprise an antisense strand thatcomprises a region of complementarity to a target RNA sequence and theregion of complementarity is in the range of 8 to 15, 8 to 30, 8 to 40,or 10 to 50, or 5 to 50, or 5 to 40 nucleotides in length. In someembodiments, a region of complementarity is 5, 6, 7, 8, 9, 10, 11, 12,13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30,31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48,49, or 50 nucleotides in length. In some embodiments, the region ofcomplementarity is complementary with at least 6, at least 7, at least8, at least 9, at least 10, at least 11, at least 12, at least 13, atleast 14, at least 15, at least 16, at least 17, at least 18, at least19, at least 20, at least 21, at least 22, at least 23, at least 24, atleast 25 or more consecutive nucleotides of a target RNA sequence. Insome embodiments, siRNA molecules comprise a nucleotide sequence thatcontains no more than 1, 2, 3, 4, or 5 base mismatches compared to theportion of the consecutive nucleotides of target RNA sequence. In someembodiments, siRNA molecules comprise a nucleotide sequence that has upto 3 mismatches over 15 bases, or up to 2 mismatches over 10 bases.

In some embodiments, siRNA molecules comprise an antisense strandcomprising a nucleotide sequence that is complementary (e.g., at least85%, at least 90%, at least 95%, or 100%) to the target RNA sequence ofthe oligonucleotides provided herein. In some embodiments, siRNAmolecules comprise an antisense strand comprising a nucleotide sequencethat is at least 85%, at least 90%, at least 95%, or 100% identical tothe oligonucleotides provided herein. In some embodiments, siRNAmolecules comprise an antisense strand comprising at least 6, at least7, at least 8, at least 9, at least 10, at least 11, at least 12, atleast 13, at least 14, at least 15, at least 16, at least 17, at least18, at least 19, at least 20, at least 21, at least 22, at least 23, atleast 24, at least 25 or more consecutive nucleotides of theoligonucleotides provided herein.

Double-stranded siRNA may comprise sense and antisense RNA strands thatare the same length or different lengths. Double-stranded siRNAmolecules can also be assembled from a single oligonucleotide in astem-loop structure, wherein self-complementary sense and antisenseregions of the siRNA molecule are linked by means of a nucleic acidbased or non-nucleic acid-based linker(s), as well as circularsingle-stranded RNA having two or more loop structures and a stemcomprising self-complementary sense and antisense strands, wherein thecircular RNA can be processed either in vivo or in vitro to generate anactive siRNA molecule capable of mediating RNAi. Small hairpin RNA(shRNA) molecules thus are also contemplated herein. These moleculescomprise a specific antisense sequence in addition to the reversecomplement (sense) sequence, typically separated by a spacer or loopsequence. Cleavage of the spacer or loop provides a single-stranded RNAmolecule and its reverse complement, such that they may anneal to form adsRNA molecule (optionally with additional processing steps that mayresult in addition or removal of one, two, three or more nucleotidesfrom the 3′ end and/or (e.g., and) the 5′ end of either or bothstrands). A spacer can be of a sufficient length to permit the antisenseand sense sequences to anneal and form a double-stranded structure (orstem) prior to cleavage of the spacer (and, optionally, subsequentprocessing steps that may result in addition or removal of one, two,three, four, or more nucleotides from the 3′ end and/or (e.g., and) the5′ end of either or both strands). A spacer sequence may be an unrelatednucleotide sequence that is situated between two complementarynucleotide sequence regions which, when annealed into a double-strandednucleic acid, comprise a shRNA.

The overall length of the siRNA molecules can vary from about 14 toabout 100 nucleotides depending on the type of siRNA molecule beingdesigned. Generally between about 14 and about 50 of these nucleotidesare complementary to the RNA target sequence, i.e. constitute thespecific antisense sequence of the siRNA molecule. For example, when thesiRNA is a double- or single-stranded siRNA, the length can vary fromabout 14 to about 50 nucleotides, whereas when the siRNA is a shRNA orcircular molecule, the length can vary from about 40 nucleotides toabout 100 nucleotides.

An siRNA molecule may comprise a 3′ overhang at one end of the molecule.The other end may be blunt-ended or have also an overhang (5′ or 3′).When the siRNA molecule comprises an overhang at both ends of themolecule, the length of the overhangs may be the same or different. Inone embodiment, the siRNA molecule of the present disclosure comprises3′ overhangs of about 1 to about 3 nucleotides on both ends of themolecule. In some embodiments, the siRNA molecule comprises 3′ overhangsof about 1 to about 3 nucleotides on the sense strand. In someembodiments, the siRNA molecule comprises 3′ overhangs of about 1 toabout 3 nucleotides on the antisense strand. In some embodiments, thesiRNA molecule comprises 3′ overhangs of about 1 to about 3 nucleotideson both the sense strand and the antisense strand.

In some embodiments, the siRNA molecule comprises one or more modifiednucleotides (e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more). In someembodiments, the siRNA molecule comprises one or more modifiednucleotides and/or (e.g., and) one or more modified internucleotidelinkages. In some embodiments, the modified nucleotide comprises amodified sugar moiety (e.g. a 2′ modified nucleotide). In someembodiments, the siRNA molecule comprises one or more 2′ modifiednucleotides, e.g., a 2′-deoxy, 2′-fluoro (2′-F), 2′-O-methyl (2′-O-Me),2′-O-methoxyethyl (2′-MOE), 2′-O-aminopropyl (2′-O-AP),2′-O-dimethylaminoethyl (2′-O-DMAOE), 2′-O-dimethylaminopropyl(2′-O-DMAP), 2′-O-dimethylaminoethyloxyethyl (2′-O-DMAEOE), or2′-O—N-methylacetamido (2′-O-NMA). In some embodiments, each nucleotideof the siRNA molecule is a modified nucleotide (e.g., a 2′-modifiednucleotide). In some embodiments, the siRNA molecule comprises one ormore phosphorodiamidate morpholinos. In some embodiments, eachnucleotide of the siRNA molecule is a phosphorodiamidate morpholino.

In some embodiments, the siRNA molecule contains a phosphorothioate orother modified internucleotide linkage. In some embodiments, the siRNAmolecule comprises phosphorothioate internucleoside linkages. In someembodiments, the siRNA molecule comprises phosphorothioateinternucleoside linkages between at least two nucleotides. In someembodiments, the siRNA molecule comprises phosphorothioate internucleoside linkages between all nucleotides. For example, in some embodiments,the siRNA molecule comprises modified internucleotide linkages at thefirst, second, and/or (e.g., and) third internucleoside linkage at the5′ or 3′ end of the siRNA molecule.

In some embodiments, the modified internucleotide linkages arephosphorus-containing linkages. In some embodiments,phosphorus-containing linkages that may be used include, but are notlimited to, phosphorothioates, chiral phosphorothioates,phosphorodithioates, phosphotriesters, aminoalkylphosphotriesters,methyl and other alkyl phosphonates comprising 3′alkylene phosphonatesand chiral phosphonates, phosphinates, phosphoramidates comprising3′-amino phosphoramidate and aminoalkylphosphoramidates,thionophosphoramidates, thionoalkylphosphonates,thionoalkylphosphotriesters, and boranophosphates having normal 3′-5′linkages, 2′-5′ linked analogs of these, and those having invertedpolarity wherein the adjacent pairs of nucleoside units are linked 3′-5′to 5′-3′ or 2′-5′ to 5′-2′; see U.S. Pat. Nos. 3,687,808; 4,469,863;4,476,301; 5,023,243; 5,177,196; 5,188,897; 5,264,423; 5,276,019;5,278,302; 5,286,717; 5,321,131; 5,399,676; 5,405,939; 5,453,496; 5,455,233; 5,466,677; 5,476,925; 5,519,126; 5,536,821; 5,541,306; 5,550,111;5,563, 253; 5,571,799; 5,587,361; and 5,625,050.

Any of the modified chemistries or formats of siRNA molecules describedherein can be combined with each other. For example, one, two, three,four, five, or more different types of modifications can be includedwithin the same siRNA molecule.

In some embodiments, the antisense strand comprises one or more modifiednucleotides (e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more). In someembodiments, the antisense strand comprises one or more modifiednucleotides and/or (e.g., and) one or more modified internucleotidelinkages. In some embodiments, the modified nucleotide comprises amodified sugar moiety (e.g. a 2′ modified nucleotide). In someembodiments, the antisense strand comprises one or more 2′ modifiednucleotides, e.g., a 2′-deoxy, 2′-fluoro (2′-F), 2′-O-methyl (2′-O-Me),2′-O-methoxyethyl (2′-MOE), 2′-O-aminopropyl (2′-O-AP),2′-O-dimethylaminoethyl (2′-O-DMAOE), 2′-O-dimethylaminopropyl(2′-O-DMAP), 2′-O-dimethylaminoethyloxyethyl (2′-O-DMAEOE), or2′-O—N-methylacetamido (2′-O-NMA). In some embodiments, each nucleotideof the antisense strand is a modified nucleotide (e.g., a 2′-modifiednucleotide). In some embodiments, the antisense strand comprises one ormore phosphorodiamidate morpholinos. In some embodiments, the antisensestrand is a phosphorodiamidate morpholino oligomer (PMO).

In some embodiments, antisense strand contains a phosphorothioate orother modified internucleotide linkage. In some embodiments, theantisense strand comprises phosphorothioate internucleoside linkages. Insome embodiments, the antisense strand comprises phosphorothioateinternucleoside linkages between at least two nucleotides. In someembodiments, the antisense strand comprises phosphorothioateinternucleoside linkages between all nucleotides. For example, in someembodiments, the antisense strand comprises modified internucleotidelinkages at the first, second, and/or (e.g., and) third internucleosidelinkage at the 5′ or 3′ end of the siRNA molecule. In some embodiments,the modified internucleotide linkages are phosphorus-containinglinkages. In some embodiments, phosphorus-containing linkages that maybe used include, but are not limited to, phosphorothioates, chiralphosphorothioates, phosphorodithioates, phosphotriesters,aminoalkylphosphotriesters, methyl and other alkyl phosphonatescomprising 3′alkylene phosphonates and chiral phosphonates,phosphinates, phosphoramidates comprising 3′-amino phosphoramidate andaminoalkylphosphoramidates, thionophosphoramidates,thionoalkylphosphonates, thionoalkylphosphotriesters, andboranophosphates having normal 3′-5′ linkages, 2′-5′ linked analogs ofthese, and those having inverted polarity wherein the adjacent pairs ofnucleoside units are linked 3′-5′ to 5′-3′ or 2′-5′ to 5′-2′; see U.S.Pat. Nos. 3,687,808; 4,469,863; 4,476,301; 5,023,243; 5,177,196;5,188,897; 5,264,423; 5,276,019; 5,278,302; 5,286,717; 5,321,131;5,399,676; 5,405,939; 5,453,496; 5,455, 233; 5,466,677; 5,476,925;5,519,126; 5,536,821; 5,541,306; 5,550,111; 5,563, 253; 5,571,799;5,587,361; and 5,625,050.

Any of the modified chemistries or formats of the antisense stranddescribed herein can be combined with each other. For example, one, two,three, four, five, or more different types of modifications can beincluded within the same antisense strand.

In some embodiments, the sense strand comprises one or more modifiednucleotides (e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more). In someembodiments, the sense strand comprises one or more modified nucleotidesand/or (e.g., and) one or more modified internucleotide linkages. Insome embodiments, the modified nucleotide comprises a modified sugarmoiety (e.g. a 2′ modified nucleotide). In some embodiments, the sensestrand comprises one or more 2′ modified nucleotides, e.g., a 2′-deoxy,2′-fluoro (2′-F), 2′-O-methyl (2′-O-Me), 2′-O-methoxyethyl (2′-MOE),2′-O-aminopropyl (2′-O-AP), 2′-O-dimethylaminoethyl (2′-O-DMAOE),2′-O-dimethylaminopropyl (2′-O-DMAP), 2′-O-dimethylaminoethyloxyethyl(2′-O-DMAEOE), or 2′-O—N-methylacetamido (2′-O-NMA). In someembodiments, each nucleotide of the sense strand is a modifiednucleotide (e.g., a 2′-modified nucleotide). In some embodiments, thesense strand comprises one or more phosphorodiamidate morpholinos. Insome embodiments, the antisense strand is a phosphorodiamidatemorpholino oligomer (PMO). In some embodiments, the sense strandcontains a phosphorothioate or other modified internucleotide linkage.In some embodiments, the sense strand comprises phosphorothioateinternucleoside linkages. In some embodiments, the sense strandcomprises phosphorothioate internucleoside linkages between at least twonucleotides. In some embodiments, the sense strand comprisesphosphorothioate internucleoside linkages between all nucleotides. Forexample, in some embodiments, the sense strand comprises modifiedinternucleotide linkages at the first, second, and/or (e.g., and) thirdinternucleoside linkage at the 5′ or 3′ end of the sense strand.

In some embodiments, the modified internucleotide linkages arephosphorus-containing linkages. In some embodiments,phosphorus-containing linkages that may be used include, but are notlimited to, phosphorothioates, chiral phosphorothioates,phosphorodithioates, phosphotriesters, aminoalkylphosphotriesters,methyl and other alkyl phosphonates comprising 3′alkylene phosphonatesand chiral phosphonates, phosphinates, phosphoramidates comprising3′-amino phosphoramidate and aminoalkylphosphoramidates,thionophosphoramidates, thionoalkylphosphonates,thionoalkylphosphotriesters, and boranophosphates having normal 3′-5′linkages, 2′-5′ linked analogs of these, and those having invertedpolarity wherein the adjacent pairs of nucleoside units are linked 3′-5′to 5′-3′ or 2′-5′ to 5′-2′; see U.S. Pat. Nos. 3,687,808; 4,469,863;4,476,301; 5,023,243; 5,177,196; 5,188,897; 5,264,423; 5,276,019;5,278,302; 5,286,717; 5,321,131; 5,399,676; 5,405,939; 5,453,496; 5,455,233; 5,466,677; 5,476,925; 5,519,126; 5,536,821; 5,541,306; 5,550,111;5,563, 253; 5,571,799; 5,587,361; and 5,625,050.

Any of the modified chemistries or formats of the sense strand describedherein can be combined with each other. For example, one, two, three,four, five, or more different types of modifications can be includedwithin the same sense strand.

In some embodiments, the antisense or sense strand of the siRNA moleculecomprises modifications that enhance or reduce RNA-induced silencingcomplex (RISC) loading. In some embodiments, the antisense strand of thesiRNA molecule comprises modifications that enhance RISC loading. Insome embodiments, the sense strand of the siRNA molecule comprisesmodifications that reduce RISC loading and reduce off-target effects. Insome embodiments, the antisense strand of the siRNA molecule comprises a2′-O-methoxyethyl (2′-MOE) modification. The addition of the2′-O-methoxyethyl (2′-MOE) group at the cleavage site improves both thespecificity and silencing activity of siRNAs by facilitating theoriented RNA-induced silencing complex (RISC) loading of the modifiedstrand, as described in Song et al., (2017) Mol Ther Nucleic Acids9:242-250, incorporated herein by reference in its entirety. In someembodiments, the antisense strand of the siRNA molecule comprises a2′-OMe-phosphorodithioate modification, which increases RISC loading asdescribed in Wu et al., (2014) Nat Commun 5:3459, incorporated herein byreference in its entirety.

In some embodiments, the sense strand of the siRNA molecule comprises a5′-morpholino, which reduces RISC loading of the sense strand andimproves antisense strand selection and RNAi activity, as described inKumar et al., (2019) Chem Commun (Camb) 55(35):5139-5142, incorporatedherein by reference in its entirety. In some embodiments, the sensestrand of the siRNA molecule is modified with a synthetic RNA-like highaffinity nucleotide analogue, Locked Nucleic Acid (LNA), which reducesRISC loading of the sense strand and further enhances antisense strandincorporation into RISC, as described in Elman et al., (2005) NucleicAcids Res. 33(1): 439-447, incorporated herein by reference in itsentirety. In some embodiments, the sense strand of the siRNA moleculecomprises a 5′ unlocked nucleic acid (UNA) modification, which reduceRISC loading of the sense strand and improve silencing potency of theantisense strand, as described in Snead et al., (2013) Mol Ther NucleicAcids 2(7):e103, incorporated herein by reference in its entirety. Insome embodiments, the sense strand of the siRNA molecule comprises a5-nitroindole modification, which descreased the RNAi potency of thesense strand and reduces off-target effects as described in Zhang etal., (2012) Chembiochem 13(13):1940-1945, incorporated herein byreference in its entirety. In some embodiments, the sense strandcomprises a 2′-O′methyl (2′-O-Me) modification, which reduces RISCloading and the off-target effects of the sense strand, as described inZheng et al., FASEB (2013) 27(10): 4017-4026, incorporated herein byreference in its entirety. In some embodiments, the sense strand of thesiRNA molecule is fully substituted with morpholino, 2′-MOE or 2′-O-Meresidues, and are not recognized by RISC as described in Kole et al.,(2012) Nature reviews. Drug Discovery 11(2):125-140, incorporated hereinby reference in its entirety. In some embodiments the antisense strandof the siRNA molecule comprises a 2′-MOE modification and the sensestrand comprises a 2′-O-Me modification (see e.g., Song et al., (2017)Mol Ther Nucleic Acids 9:242-250). In some embodiments at least one(e.g., at least 2, at least 3, at least 4, at least 5, at least 10)siRNA molecule is linked (e.g., covalently) to a muscle-targeting agent.In some embodiments, the muscle-targeting agent may comprise, or consistof, a nucleic acid (e.g., DNA or RNA), a peptide (e.g., an antibody), alipid (e.g., a microvesicle), or a sugar moiety (e.g., apolysaccharide). In some embodiments, the muscle-targeting agent is anantibody. In some embodiments, the muscle-targeting agent is ananti-transferrin receptor antibody (e.g., any one of the anti-TfRantibodies provided herein). In some embodiments, the muscle-targetingagent may be linked to the 5′ end of the sense strand of the siRNAmolecule. In some embodiments, the muscle-targeting agent may be linkedto the 3′ end of the sense strand of the siRNA molecule. In someembodiments, the muscle-targeting agent may be linked internally to thesense strand of the siRNA molecule. In some embodiments, themuscle-targeting agent may be linked to the 5′ end of the antisensestrand of the siRNA molecule. In some embodiments, the muscle-targetingagent may be linked to the 3′ end of the antisense strand of the siRNAmolecule. In some embodiments, the muscle-targeting agent may be linkedinternally to the antisense strand of the siRNA molecule.

k. microRNA (miRNAs)

In some embodiments, an oligonucleotide may be a microRNA (miRNA).MicroRNAs (referred to as “miRNAs”) are small non-coding RNAs, belongingto a class of regulatory molecules that control gene expression bybinding to complementary sites on a target RNA transcript. Typically,miRNAs are generated from large RNA precursors (termed pri-miRNAs) thatare processed in the nucleus into approximately 70 nucleotidepre-miRNAs, which fold into imperfect stem-loop structures. Thesepre-miRNAs typically undergo an additional processing step within thecytoplasm where mature miRNAs of 18-25 nucleotides in length are excisedfrom one side of the pre-miRNA hairpin by an RNase III enzyme, Dicer.

As used herein, miRNAs including pri-miRNA, pre-miRNA, mature miRNA orfragments of variants thereof that retain the biological activity ofmature miRNA. In one embodiment, the size range of the miRNA can be from21 nucleotides to 170 nucleotides. In one embodiment the size range ofthe miRNA is from 70 to 170 nucleotides in length. In anotherembodiment, mature miRNAs of from 21 to 25 nucleotides in length can beused.

l. Aptamers

In some embodiments, oligonucleotides provided herein may be in the formof aptamers. Generally, in the context of molecular payloads, aptamer isany nucleic acid that binds specifically to a target, such as a smallmolecule, protein, nucleic acid in a cell. In some embodiments, theaptamer is a DNA aptamer or an RNA aptamer. In some embodiments, anucleic acid aptamer is a single-stranded DNA or RNA (ssDNA or ssRNA).It is to be understood that a single-stranded nucleic acid aptamer mayform helices and/or (e.g., and) loop structures. The nucleic acid thatforms the nucleic acid aptamer may comprise naturally occurringnucleotides, modified nucleotides, naturally occurring nucleotides withhydrocarbon linkers (e.g., an alkylene) or a polyether linker (e.g., aPEG linker) inserted between one or more nucleotides, modifiednucleotides with hydrocarbon or PEG linkers inserted between one or morenucleotides, or a combination of thereof. Exemplary publications andpatents describing aptamers and method of producing aptamers include,e.g., Lorsch and Szostak, 1996; Jayasena, 1999; U.S. Pat. Nos.5,270,163; 5,567,588; 5,650,275; 5,670,637; 5,683,867; 5,696,249;5,789,157; 5,843,653; 5,864,026; 5,989,823; 6,569,630; 8,318,438 and PCTapplication WO 99/31275, each incorporated herein by reference.

m. Ribozymes

In some embodiments, oligonucleotides provided herein may be in the formof a ribozyme. A ribozyme (ribonucleic acid enzyme) is a molecule,typically an RNA molecule, that is capable of performing specificbiochemical reactions, similar to the action of protein enzymes.Ribozymes are molecules with catalytic activities including the abilityto cleave at specific phosphodiester linkages in RNA molecules to whichthey have hybridized, such as mRNAs, RNA-containing substrates, lncRNAs,and ribozymes, themselves.

Ribozymes may assume one of several physical structures, one of which iscalled a “hammerhead.” A hammerhead ribozyme is composed of a catalyticcore containing nine conserved bases, a double-stranded stem and loopstructure (stem-loop II), and two regions complementary to the targetRNA flanking regions the catalytic core. The flanking regions enable theribozyme to bind to the target RNA specifically by formingdouble-stranded stems I and III. Cleavage occurs in cis (i.e., cleavageof the same RNA molecule that contains the hammerhead motif) or in trans(cleavage of an RNA substrate other than that containing the ribozyme)next to a specific ribonucleotide triplet by a transesterificationreaction from a 3′, 5′-phosphate diester to a 2′, 3′-cyclic phosphatediester. Without wishing to be bound by theory, it is believed that thiscatalytic activity requires the presence of specific, highly conservedsequences in the catalytic region of the ribozyme.

Modifications in ribozyme structure have also included the substitutionor replacement of various non-core portions of the molecule withnon-nucleotidic molecules. For example, Benseler et al. (J. Am. Chem.Soc. (1993) 115:8483-8484) disclosed hammerhead-like molecules in whichtwo of the base pairs of stem II, and all four of the nucleotides ofloop II were replaced with non-nucleoside linkers based on hexaethyleneglycol, propanediol, bis(triethylene glycol) phosphate,tris(propanediol)bisphosphate, or bis(propanediol) phosphate. Ma et al.(Biochem. (1993) 32:1751-1758; Nucleic Acids Res. (1993) 21:2585-2589)replaced the six nucleotide loop of the TAR ribozyme hairpin withnon-nucleotidic, ethylene glycol-related linkers. Thomson et al.(Nucleic Acids Res. (1993) 21:5600-5603) replaced loop II with linear,non-nucleotidic linkers of 13, 17, and 19 atoms in length.

Ribozyme oligonucleotides can be prepared using well known methods (see,e.g., PCT Publications WO9118624; WO9413688; WO9201806; and WO 92/07065;and U.S. Pat. Nos. 5,436,143 and 5,650,502) or can be purchased fromcommercial sources (e.g., US Biochemicals) and, if desired, canincorporate nucleotide analogs to increase the resistance of theoligonucleotide to degradation by nucleases in a cell. The ribozyme maybe synthesized in any known manner, e.g., by use of a commerciallyavailable synthesizer produced, e.g., by Applied Biosystems, Inc. orMilligen. The ribozyme may also be produced in recombinant vectors byconventional means. See, Molecular Cloning: A Laboratory Manual, ColdSpring Harbor Laboratory (Current edition). The ribozyme RNA sequencesmaybe synthesized conventionally, for example, by using RNA polymerasessuch as T7 or SP6.

n. Guide Nucleic Acids

In some embodiments, oligonucleotides are guide nucleic acid, e.g.,guide RNA (gRNA) molecules. Generally, a guide RNA is a short syntheticRNA composed of (1) a scaffold sequence that binds to a nucleic acidprogrammable DNA binding protein (napDNAbp), such as Cas9, and (2) anucleotide spacer portion that defines the DNA target sequence (e.g.,genomic DNA target) to which the gRNA binds in order to bring thenucleic acid programmable DNA binding protein in proximity to the DNAtarget sequence. In some embodiments, the napDNAbp is a nucleicacid-programmable protein that forms a complex with (e.g., binds orassociates with) one or more RNA(s) that targets the nucleicacid-programmable protein to a target DNA sequence (e.g., a targetgenomic DNA sequence). In some embodiments, a nucleic acid-programmablenuclease, when in a complex with an RNA, may be referred to as anuclease:RNA complex. Guide RNAs can exist as a complex of two or moreRNAs, or as a single RNA molecule.

Guide RNAs (gRNAs) that exist as a single RNA molecule may be referredto as single-guide RNAs (sgRNAs), though gRNA is also used to refer toguide RNAs that exist as either single molecules or as a complex of twoor more molecules. Typically, gRNAs that exist as a single RNA speciescomprise two domains: (1) a domain that shares homology to a targetnucleic acid (i.e., directs binding of a Cas9 complex to the target);and (2) a domain that binds a Cas9 protein. In some embodiments, domain(2) corresponds to a sequence known as a tracrRNA and comprises astem-loop structure. In some embodiments, domain (2) is identical orhomologous to a tracrRNA as provided in Jinek et al., Science337:816-821 (2012), the entire contents of which is incorporated hereinby reference.

In some embodiments, a gRNA comprises two or more of domains (1) and(2), and may be referred to as an extended gRNA. For example, anextended gRNA will bind two or more Cas9 proteins and bind a targetnucleic acid at two or more distinct regions, as described herein. ThegRNA comprises a nucleotide sequence that complements a target site,which mediates binding of the nuclease/RNA complex to said target site,providing the sequence specificity of the nuclease:RNA complex. In someembodiments, the RNA-programmable nuclease is the (CRISPR-associatedsystem) Cas9 endonuclease, for example, Cas9 (Csn1) from Streptococcuspyogenes (see, e.g., “Complete genome sequence of an M1 strain ofStreptococcus pyogenes.” Ferretti J. J., McShan W. M., Ajdic D. J.,Savic D. J., Savic G., Lyon K., Primeaux C., Sezate S., Suvorov A. N.,Kenton S., Lai H. S., Lin S. P., Qian Y., Jia H. G., Najar F. Z., RenQ., Zhu H., Song L., White J., Yuan X., Clifton S. W., Roe B. A.,McLaughlin R. E., Proc. Natl. Acad. Sci. U.S.A. 98:4658-4663 (2001);“CRISPR RNA maturation by trans-encoded small RNA and host factor RNaseIII.” Deltcheva E., Chylinski K., Sharma C. M., Gonzales K., Chao Y.,Pirzada Z. A., Eckert M. R., Vogel J., Charpentier E., Nature471:602-607 (2011); and “A programmable dual-RNA-guided DNA endonucleasein adaptive bacterial immunity.” Jinek M., Chylinski K., Fonfara I.,Hauer M., Doudna J. A., Charpentier E. Science 337:816-821 (2012), theentire contents of each of which are incorporated herein by reference.

o. Multimers

In some embodiments, molecular payloads may comprise multimers (e.g.,concatemers) of 2 or more oligonucleotides connected by a linker. Inthis way, in some embodiments, the oligonucleotide loading of acomplex/conjugate can be increased beyond the available linking sites ona targeting agent (e.g., available thiol sites on an antibody) orotherwise tuned to achieve a particular payload loading content.Oligonucleotides in a multimer can be the same or different (e.g.,targeting different genes or different sites on the same gene orproducts thereof).

In some embodiments, multimers comprise 2 or more oligonucleotideslinked together by a cleavable linker. However, in some embodiments,multimers comprise 2 or more oligonucleotides linked together by anon-cleavable linker. In some embodiments, a multimer comprises 2, 3, 4,5, 6, 7, 8, 9, 10 or more oligonucleotides linked together. In someembodiments, a multimer comprises 2 to 5, 2 to 10 or 4 to 20oligonucleotides linked together.

In some embodiments, a multimer comprises 2 or more oligonucleotideslinked end-to-end (in a linear arrangement). In some embodiments, amultimer comprises 2 or more oligonucleotides linked end-to-end via anoligonucleotide based linker (e.g., poly-dT linker, an abasic linker).In some embodiments, a multimer comprises a 5′ end of oneoligonucleotide linked to a 3′ end of another oligonucleotide. In someembodiments, a multimer comprises a 3′ end of one oligonucleotide linkedto a 3′ end of another oligonucleotide. In some embodiments, a multimercomprises a 5′ end of one oligonucleotide linked to a 5′ end of anotheroligonucleotide. Still, in some embodiments, multimers can comprise abranched structure comprising multiple oligonucleotides linked togetherby a branching linker.

Further examples of multimers that may be used in the complexes providedherein are disclosed, for example, in US Patent Application Number2015/0315588 A1, entitled Methods of delivering multiple targetingoligonucleotides to a cell using cleavable linkers, which was publishedon Nov. 5, 2015; US Patent Application Number 2015/0247141 A1, entitledMultimeric Oligonucleotide Compounds, which was published on Sep. 3,2015, US Patent Application Number US 2011/0158937 A1, entitledImmunostimulatory Oligonucleotide Multimers, which was published on Jun.30, 2011; and U.S. Pat. No. 5,693,773, entitled Triplex-FormingAntisense Oligonucleotides Having Abasic Linkers Targeting Nucleic AcidsComprising Mixed Sequences Of Purines And Pyrimidines, which issued onDec. 2, 1997, the contents of each of which are incorporated herein byreference in their entireties.

ii. Small Molecules:

Any suitable small molecule may be used as a molecular payload, asdescribed herein. In some embodiments, the small molecule is asdescribed in US Patent Application Publication 20170340606, published onNov. 30, 2017, entitled “METHODS OF TREATING MUSCULAR DYSTROPHY” or asdescribed in US Patent Application Publication 20180050043, published onFeb. 22, 2018, entitled “INHIBITION OF DUX4 EXPRESSION USING BROMODOMAINAND EXTRA-TERMINAL DOMAIN PROTEIN INHIBITORS (BETi). Further examples ofsmall molecule payloads are provided in Bosnakovski, D., et al.,High-throughput screening identifies inhibitors of DUX4-induced myoblasttoxicity, Skelet Muscle, February 2014, and Choi. S., et al.,“Transcriptional Inhibitors Identified in a 160,000-CompoundSmall-Molecule DUX4 Viability Screen,” Journal of BiomolecularScreening, 2016. For example, in some embodiments, the small molecule isa transcriptional inhibitor, such as SHC351, SHC540, SHC572. In someembodiments, the small molecule is STR00316 increases production oractivity of another protein, such as integrin. In some embodiments, thesmall molecule is a bromodomain inhibitor (BETi), such as JQ1, PF1-1,I-BET-762, I-BET-151, RVX-208, or CPI-0610.

iii. Peptides

Any suitable peptide or protein may be used as a molecular payload, asdescribed herein. In some embodiments, a protein is an enzyme. Thesepeptides or proteins may be produced, synthesized, and/or (e.g., and)derivatized using several methodologies, e.g. phage displayed peptidelibraries, one-bead one-compound peptide libraries, or positionalscanning synthetic peptide combinatorial libraries. In some embodiments,the peptide or protein may bind a DME1 or DME2 enhancer to inhibit DUX4expression, e.g., by blocking binding of an activator.

iv. Nucleic Acid Constructs

Any suitable gene expression construct may be used as a molecularpayload, as described herein. In some embodiments, a gene expressionconstruct may be a vector or a cDNA fragment. In some embodiments, agene expression construct may be messenger RNA (mRNA). In someembodiments, a mRNA used herein may be a modified mRNA, e.g., asdescribed in U.S. Pat. No. 8,710,200, issued on Apr. 24, 2014, entitled“Engineered nucleic acids encoding a modified erythropoietin and theirexpression”. In some embodiments, a mRNA may comprise a 5′ methyl cap.In some embodiments, a mRNA may comprise a polyA tail, optionally of upto 160 nucleotides in length. In some embodiments, the gene expressionconstruct may be expressed, e.g., overexpressed, within the nucleus of amuscle cell. In some embodiments, the gene expression construct encodesa oligonucleotide (e.g., an shRNA targeting DUX4) or a protein thatdownregulates the expression of DUX4 (e.g., a peptide or protein thatbinds to DME1 or DME2 enhancer to inhibit DUX4 expression, e.g., byblocking binding of an activator). In some embodiments, the geneexpression construct encodes a oligonucleotide (e.g., an shRNA targetingMuRF1 or MAFbx) that downregulates the expression of MuRF1 or MAFbx,respectively. In some embodiments, the gene expression constructs encodea protein that comprises at least one zinc finger. In some embodiments,the gene expression construct encodes a gene editing enzyme. Additionalexamples of nucleic acid constructs that may be used as molecularpayloads are provided in International Patent Application PublicationWO2017152149A1, published on Sep. 19, 2017, entitled, “CLOSED-ENDEDLINEAR DUPLEX DNA FOR NON-VIRAL GENE TRANSFER”; U.S. Pat. No.8,853,377B2, issued on Oct. 7, 2014, entitled, “MRNA FOR USE INTREATMENT OF HUMAN GENETIC DISEASES”; and U.S. Pat. No. 8,822,663B2,issued on Sep. 2, 2014, ENGINEERED NUCLEIC ACIDS AND METHODS OF USETHEREOF,” the contents of each of which are incorporated herein byreference in their entireties.

C. Linkers

Complexes described herein generally comprise a linker that connects anyone of the anti-TfR antibodies described herein to a molecular payload.A linker comprises at least one covalent bond. In some embodiments, alinker may be a single bond, e.g., a disulfide bond or disulfide bridge,that connects an anti-TfR antibody to a molecular payload. However, insome embodiments, a linker may connect any one of the anti-TfRantibodies described herein to a molecular payload through multiplecovalent bonds. In some embodiments, a linker may be a cleavable linker.However, in some embodiments, a linker may be a non-cleavable linker. Alinker is generally stable in vitro and in vivo, and may be stable incertain cellular environments. Additionally, generally a linker does notnegatively impact the functional properties of either the anti-TfRantibody or the molecular payload. Examples and methods of synthesis oflinkers are known in the art (see, e.g. Kline, T. et al. “Methods toMake Homogenous Antibody Drug Conjugates.” Pharmaceutical Research,2015, 32:11, 3480-3493.; Jain, N. et al. “Current ADC Linker Chemistry”Pharm Res. 2015, 32:11, 3526-3540.; McCombs, J. R. and Owen, S. C.“Antibody Drug Conjugates: Design and Selection of Linker, Payload andConjugation Chemistry” AAPS J. 2015, 17:2, 339-351.).

A precursor to a linker typically will contain two different reactivespecies that allow for attachment to both the anti-TfR antibody and amolecular payload. In some embodiments, the two different reactivespecies may be a nucleophile and/or (e.g., and) an electrophile. In someembodiments, a linker is connected to an anti-TfR antibody viaconjugation to a lysine residue or a cysteine residue of the anti-TfRantibody. In some embodiments, a linker is connected to a cysteineresidue of an anti-TfR antibody via a maleimide-containing linker,wherein optionally the maleimide-containing linker comprises amaleimidocaproyl or maleimidomethyl cyclohexane-1-carboxylate group. Insome embodiments, a linker is connected to a cysteine residue of ananti-TfR antibody or thiol functionalized molecular payload via a3-arylpropionitrile functional group. In some embodiments, a linker isconnected to a lysine residue of an anti-TfR antibody. In someembodiments, a linker is connected to an anti-TfR antibody and/or (e.g.,and) a molecular payload via an amide bond, a carbamate bond, ahydrazide, a trizaole, a thioether, or a disulfide bond.

i. Cleavable Linkers

A cleavable linker may be a protease-sensitive linker, a pH-sensitivelinker, or a glutathione-sensitive linker. These linkers are generallycleavable only intracellularly and are preferably stable inextracellular environments, e.g. extracellular to a muscle cell.

Protease-sensitive linkers are cleavable by protease enzymatic activity.These linkers typically comprise peptide sequences and may be 2-10 aminoacids, about 2-5 amino acids, about 5-10 amino acids, about 10 aminoacids, about 5 amino acids, about 3 amino acids, or about 2 amino acidsin length. In some embodiments, a peptide sequence may comprisenaturally-occurring amino acids, e.g. cysteine, alanine, ornon-naturally-occurring or modified amino acids. Non-naturally occurringamino acids include (3-amino acids, homo-amino acids, prolinederivatives, 3-substituted alanine derivatives, linear core amino acids,N-methyl amino acids, and others known in the art. In some embodiments,a protease-sensitive linker comprises a valine-citrulline oralanine-citrulline dipeptide sequence. In some embodiments, aprotease-sensitive linker can be cleaved by a lysosomal protease, e.g.cathepsin B, and/or (e.g., and) an endosomal protease.

A pH-sensitive linker is a covalent linkage that readily degrades inhigh or low pH environments. In some embodiments, a pH-sensitive linkermay be cleaved at a pH in a range of 4 to 6. In some embodiments, apH-sensitive linker comprises a hydrazone or cyclic acetal. In someembodiments, a pH-sensitive linker is cleaved within an endosome or alysosome.

In some embodiments, a glutathione-sensitive linker comprises adisulfide moiety. In some embodiments, a glutathione-sensitive linker iscleaved by a disulfide exchange reaction with a glutathione speciesinside a cell. In some embodiments, the disulfide moiety furthercomprises at least one amino acid, e.g. a cysteine residue.

In some embodiments, the linker is a Val-cit linker (e.g., as describedin U.S. Pat. No. 6,214,345, incorporated herein by reference). In someembodiments, before conjugation, the val-cit linker has a structure of:

In some embodiments, after conjugation, the val-cit linker has astructure of:

In some embodiments, the Val-cit linker is attached to a reactivechemical moiety (e.g., SPAAC for click chemistry conjugation). In someembodiments, before click chemistry conjugation, the val-cit linkerattached to a reactive chemical moiety (e.g., SPAAC for click chemistryconjugation) has the structure of:

wherein n is any number from 0-10. In some embodiments, n is 3.

In some embodiments, the val-cit linker attached to a reactive chemicalmoiety (e.g., SPAAC for click chemistry conjugation) is conjugated(e.g., via a different chemical moiety) to a molecular payload (e.g., anoligonucleotide). In some embodiments, the val-cit linker attached to areactive chemical moiety (e.g., SPAAC for click chemistry conjugation)and conjugated to a molecular payload (e.g., an oligonucleotide) has thestructure of (before click chemistry conjugation):

wherein n is any number from 0-10. In some embodiments, n is 3.

In some embodiments, after conjugation to a molecular payload (e.g., anoligonucleotide), the val-cit linker has a structure of:

wherein n is any number from 0-10, and wherein m is any number from0-10. In some embodiments, n is 3 and m is 4.

ii. Non-Cleavable Linkers

In some embodiments, non-cleavable linkers may be used. Generally, anon-cleavable linker cannot be readily degraded in a cellular orphysiological environment. In some embodiments, a non-cleavable linkercomprises an optionally substituted alkyl group, wherein thesubstitutions may include halogens, hydroxyl groups, oxygen species, andother common substitutions. In some embodiments, a linker may comprisean optionally substituted alkyl, an optionally substituted alkylene, anoptionally substituted arylene, a heteroarylene, a peptide sequencecomprising at least one non-natural amino acid, a truncated glycan, asugar or sugars that cannot be enzymatically degraded, an azide, analkyne-azide, a peptide sequence comprising a LPXT sequence, athioether, a biotin, a biphenyl, repeating units of polyethylene glycolor equivalent compounds, acid esters, acid amides, sulfamides, and/or(e.g., and) an alkoxy-amine linker. In some embodiments,sortase-mediated ligation will be utilized to covalently link ananti-TfR antibody comprising a LPXT sequence to a molecular payloadcomprising a (G). sequence (see, e.g. Proft T. Sortase-mediated proteinligation: an emerging biotechnology tool for protein modification andimmobilization. Biotechnol Lett. 2010, 32(1):1-10.).

In some embodiments, a linker may comprise a substituted alkylene, anoptionally substituted alkenylene, an optionally substituted alkynylene,an optionally substituted cycloalkylene, an optionally substitutedcycloalkenylene, an optionally substituted arylene, an optionallysubstituted heteroarylene further comprising at least one heteroatomselected from N, O, and S; an optionally substituted heterocyclylenefurther comprising at least one heteroatom selected from N, O, and S; animino, an optionally substituted nitrogen species, an optionallysubstituted oxygen species O, an optionally substituted sulfur species,or a poly(alkylene oxide), e.g. polyethylene oxide or polypropyleneoxide.

iii. Linker Conjugation

In some embodiments, a linker is connected to an anti-TfR antibodyand/or (e.g., and) molecular payload via a phosphate, thioether, ether,carbon-carbon, carbamate, or amide bond. In some embodiments, a linkeris connected to an oligonucleotide through a phosphate orphosphorothioate group, e.g. a terminal phosphate of an oligonucleotidebackbone. In some embodiments, a linker is connected to an anti-TfRantibody, through a lysine or cysteine residue present on the anti-TfRantibody.

In some embodiments, a linker is connected to an anti-TfR antibodyand/or (e.g., and) molecular payload by a cycloaddition reaction betweenan azide and an alkyne to form a triazole, wherein the azide and thealkyne may be located on the anti-TfR antibody, molecular payload, orthe linker. In some embodiments, an alkyne may be a cyclic alkyne, e.g.,a cyclooctyne. In some embodiments, an alkyne may be bicyclononyne (alsoknown as bicyclo[6.1.0]nonyne or BCN) or substituted bicyclononyne. Insome embodiments, a cyclooctane is as described in International PatentApplication Publication WO2011136645, published on Nov. 3, 2011,entitled, “Fused Cyclooctyne Compounds And Their Use In Metal free ClickReactions”. In some embodiments, an azide may be a sugar or carbohydratemolecule that comprises an azide. In some embodiments, an azide may be6-azido-6-deoxygalactose or 6-azido-N-acetylgalactosamine. In someembodiments, a sugar or carbohydrate molecule that comprises an azide isas described in International Patent Application PublicationWO2016170186, published on Oct. 27, 2016, entitled, “Process For TheModification Of A Glycoprotein Using A Glycosyltransferase That Is Or IsDerived From A/3(1,4)-N-Acetylgalactosaminyltransferase”. In someembodiments, a cycloaddition reaction between an azide and an alkyne toform a triazole, wherein the azide and the alkyne may be located on theanti-TfR antibody, molecular payload, or the linker is as described inInternational Patent Application Publication WO2014065661, published onMay 1, 2014, entitled, “Modified antibody, antibody-conjugate andprocess for the preparation thereof”; or International PatentApplication Publication WO2016170186, published on Oct. 27, 2016,entitled, “Process For The Modification Of A Glycoprotein Using AGlycosyltransferase That Is Or Is Derived From Aβ(1,4)-N-Acetylgalactosaminyltransferase”.

In some embodiments, a linker further comprises a spacer, e.g., apolyethylene glycol spacer or an acyl/carbomoyl sulfamide spacer, e.g.,a HydraSpace™ spacer. In some embodiments, a spacer is as described inVerkade, J. M. M. et al., “A Polar Sulfamide Spacer SignificantlyEnhances the Manufacturability, Stability, and Therapeutic Index ofAntibody- Drug Conjugates”, Antibodies, 2018, 7, 12.

In some embodiments, a linker is connected to an anti-TfR antibodyand/or (e.g., and) molecular payload by the Diels-Alder reaction betweena dienophile and a diene/hetero-diene, wherein the dienophile and thediene/hetero-diene may be located on the anti-TfR antibody, molecularpayload, or the linker. In some embodiments a linker is connected to ananti-TfR antibody and/or (e.g., and) molecular payload by otherpericyclic reactions, e.g. ene reaction. In some embodiments, a linkeris connected to an anti-TfR antibody and/or (e.g., and) molecularpayload by an amide, thioamide, or sulfonamide bond reaction. In someembodiments, a linker is connected to an anti-TfR antibody and/or (e.g.,and) molecular payload by a condensation reaction to form an oxime,hydrazone, or semicarbazide group existing between the linker and theanti-TfR antibody and/or (e.g., and) molecular payload.

In some embodiments, a linker is connected to an anti-TfR antibodyand/or (e.g., and) molecular payload by a conjugate addition reactionsbetween a nucleophile, e.g. an amine or a hydroxyl group, and anelectrophile, e.g. a carboxylic acid, carbonate, or an aldehyde. In someembodiments, a nucleophile may exist on a linker and an electrophile mayexist on an anti-TfR antibody or molecular payload prior to a reactionbetween a linker and an anti-TfR antibody or molecular payload. In someembodiments, an electrophile may exist on a linker and a nucleophile mayexist on an anti-TfR antibody or molecular payload prior to a reactionbetween a linker and an anti-TfR antibody or molecular payload. In someembodiments, an electrophile may be an azide, pentafluorophenyl, asilicon centers, a carbonyl, a carboxylic acid, an anhydride, anisocyanate, a thioisocyanate, a succinimidyl ester, a sulfosuccinimidylester, a maleimide, an alkyl halide, an alkyl pseudohalide, an epoxide,an episulfide, an aziridine, an aryl, an activated phosphorus center,and/or (e.g., and) an activated sulfur center. In some embodiments, anucleophile may be an optionally substituted alkene, an optionallysubstituted alkyne, an optionally substituted aryl, an optionallysubstituted heterocyclyl, a hydroxyl group, an amino group, analkylamino group, an anilido group, or a thiol group.

In some embodiments, the val-cit linker attached to a reactive chemicalmoiety (e.g., SPAAC for click chemistry conjugation) is conjugated tothe anti-TfR antibody by a structure of:

wherein m is any number from 0-10. In some embodiments, m is 4.

In some embodiments, the val-cit linker attached to a reactive chemicalmoiety (e.g., SPAAC for click chemistry conjugation) is conjugated to ananti-TfR antibody having a structure of:

wherein m is any number from 0-10. In some embodiments, m is 4.

In some embodiments, the val-cit linker attached to a reactive chemicalmoiety (e.g., SPAAC for click chemistry conjugation) and conjugated toan anti-TfR antibody has a structure of:

wherein n is any number from 0-10, wherein m is any number from 0-10. Insome embodiments, n is 3 and/or (e.g., and) m is 4.

In some embodiments, the val-cit linker that links the antibody and themolecular payload has a structure of:

wherein n is any number from 0-10, wherein m is any number from 0-10. Insome embodiments, n is 3 and/or (e.g., and) m is 4. In some embodiments,n is 3 and/or (e.g., and) m is 4. In some embodiments, X is NH (e.g., NHfrom an amine group of a lysine), S (e.g., S from a thiol group of acysteine), or O (e.g., O from a hydroxyl group of a serine, threonine,or tyrosine) of the antibody.

In some embodiments, the complex described herein has a structure of:

wherein n is any number from 0-10, wherein m is any number from 0-10. Insome embodiments, n is 3 and/or (e.g., and) m is 4.

In structures formula (A), (B), (C), and (D), L1, in some embodiments,is a spacer that is a substituted or unsubstituted aliphatic,substituted or unsubstituted heteroaliphatic, substituted orunsubstituted carbocyclylene, substituted or unsubstitutedheterocyclylene, substituted or unsubstituted arylene, substituted orunsubstituted heteroarylene, —O—, —N(R^(A))—, —S—, —C(═O)—, —C(═O)O—,—C(═O)NR^(A)—, —NR^(A)C(═O)—, —NR^(A)C(═O)R^(A)—, —C(═O)R^(A)—,—NR^(A)C(═O)O—, —NR^(A)C(═O)N(R^(A))—, —OC(═O)—, —OC(═O)O—,—OC(═O)N(R^(A))—, —S(O)₂NR^(A)—, —NR^(A)S(O)₂—, or a combinationthereof. In some embodiments, L1 is

wherein the piperazine moiety links to the oligonucleotide, wherein L2is

In some embodiments, L1 is:

wherein the piperazine moiety links to the oligonucleotide.

In some embodiments, L1 is

In some embodiments, L1 is linked to a 5′ phosphate of theoligonucleotide.

In some embodiments, L1 is optional (e.g., need not be present).

In some embodiments, any one of the complexes described herein has astructure of:

wherein n is 0-15 (e.g., 3) and m is 0-15 (e.g., 4).

C. Examples of Antibody-Molecular Payload Complexes

Further provided herein are non-limiting examples of complexescomprising any one the anti-TfR antibodies described herein covalentlylinked to any of the molecular payloads (e.g., an oligonucleotide)described herein. In some embodiments, the anti-TfR antibody (e.g., anyone of the anti-TfR antibodies provided in Table 2) is covalently linkedto a molecular payload (e.g., an oligonucleotide) via a linker. Any ofthe linkers described herein may be used. In some embodiments, if themolecular payload is an oligonucleotide, the linker is linked to the 5′end, the 3′ end, or internally of the oligonucleotide. In someembodiments, the linker is linked to the anti-TfR antibody via athiol-reactive linkage (e.g., via a cysteine in the anti-TfR antibody).In some embodiments, the linker (e.g., a Val-cit linker) is linked tothe antibody (e.g., an anti-TfR antibody described herein) via an aminegroup (e.g., via a lysine in the antibody). In some embodiments, themolecular payload is a DUX4-targeting oligonucleotide (e.g., anoligonucleotide comprising the nucleotide sequence of SEQ ID NO: 151).

An example of a structure of a complex comprising an anti-TfR antibodycovalently linked to a molecular payload via a Val-cit linker isprovided below:

wherein the linker is linked to the antibody via a thiol-reactivelinkage (e.g., via a cysteine in the antibody). In some embodiments, themolecular payload is a DUX4-targeting oligonucleotide (e.g., anoligonucleotide comprising the nucleotide sequence of SEQ ID NO: 151).

Another example of a structure of a complex comprising an anti-TfRantibody covalently linked to a molecular payload via a Val-cit linkeris provided below:

wherein n is a number between 0-10, wherein m is a number between 0-10,wherein the linker is linked to the antibody via an amine group (e.g.,on a lysine residue), and/or (e.g., and) wherein the linker is linked tothe oligonucleotide (e.g., at the 5′ end, 3′ end, or internally). Insome embodiments, the linker is linked to the antibody via a lysine, thelinker is linked to the oligonucleotide at the 5′ end, n is 3, and m is4. In some embodiments, the molecular payload is an oligonucleotidecomprising a sense strand and an antisense strand, and, the linker islinked to the sense strand or the antisense strand at the 5′ end or the3′ end. In some embodiments, the molecular payload is a DUX4-targetingoligonucleotide (e.g., an oligonucleotide comprising the nucleotidesequence of SEQ ID NO: 151).

It should be appreciated that antibodies can be linked to molecularpayloads with different stochiometries, a property that may be referredto as a drug to antibody ratios (DAR) with the “drug” being themolecular payload. In some embodiments, one molecular payload is linkedto an antibody (DAR=1). In some embodiments, two molecular payloads arelinked to an antibody (DAR=2). In some embodiments, three molecularpayloads are linked to an antibody (DAR=3). In some embodiments, fourmolecular payloads are linked to an antibody (DAR=4). In someembodiments, a mixture of different complexes, each having a differentDAR, is provided. In some embodiments, an average DAR of complexes insuch a mixture may be in a range of 1 to 3, 1 to 4, 1 to 5 or more. DARmay be increased by conjugating molecular payloads to different sites onan antibody and/or (e.g., and) by conjugating multimers to one or moresites on antibody. For example, a DAR of 2 may be achieved byconjugating a single molecular payload to two different sites on anantibody or by conjugating a dimer molecular payload to a single site ofan antibody.

In some embodiments, the complex described herein comprises an anti-TfRantibody described herein (e.g., the 3-A4, 3-M12, and 5-H12 antibodiesprovided in Table 2 in a IgG or Fab form) covalently linked to amolecular payload. In some embodiments, the complex described hereincomprises an anti-TfR antibody described herein (e.g., the 3-A4, 3-M12,and 5-H12 antibodies provided in Table 2 in a IgG or Fab form)covalently linked to molecular payload via a linker (e.g., a Val-citlinker). In some embodiments, the linker (e.g., a Val-cit linker) islinked to the antibody (e.g., an anti-TfR antibody described herein) viaa thiol-reactive linkage (e.g., via a cysteine in the antibody). In someembodiments, the linker (e.g., a Val-cit linker) is linked to theantibody (e.g., an anti-TfR antibody described herein) via an aminegroup (e.g., via a lysine in the antibody). In some embodiments, themolecular payload is a DUX4-targeting oligonucleotide (e.g., anoligonucleotide comprising the nucleotide sequence of SEQ ID NO: 151).

In some embodiments, in any one of the examples of complexes describedherein, the molecular payload is a DUX4-targeting oligonucleotide (e.g.,an oligonucleotide comprising the nucleotide sequence of SEQ ID NO:151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked to a molecular payload, wherein the anti-TfRantibody comprises a CDR-H1, a CDR-H2, and a CDR-H3 that are the same asthe CDR-H1, CDR-H2, and CDR-H3 shown in Table 2; and a CDR-L1, a CDR-L2,and a CDR-L3 that are the same as the CDR-L1, CDR-L2, and CDR-L3 shownin Table 2. In some embodiments, the molecular payload is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked to a molecular payload, wherein the anti-TfRantibody comprises a VH comprising the amino acid sequence of SEQ ID NO:69, SEQ ID NO: 71, or SEQ ID NO: 72, and a VL comprising the amino acidsequence of SEQ ID NO: 70. In some embodiments, the molecular payload isa DUX4-targeting oligonucleotide (e.g., an oligonucleotide comprisingthe nucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked to a molecular payload, wherein the anti-TfRantibody comprises a VH comprising the amino acid sequence of SEQ ID NO:73 or SEQ ID NO: 76, and a VL comprising the amino acid sequence of SEQID NO: 74. In some embodiments, the molecular payload is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked to a molecular payload, wherein the anti-TfRantibody comprises a VH comprising the amino acid sequence of SEQ ID NO:73 or SEQ ID NO: 76, and a VL comprising the amino acid sequence of SEQID NO: 75. In some embodiments, the molecular payload is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked to a molecular payload, wherein the anti-TfRantibody comprises a VH comprising the amino acid sequence of SEQ ID NO:77, and a VL comprising the amino acid sequence of SEQ ID NO: 78. Insome embodiments, the molecular payload is a DUX4-targetingoligonucleotide (e.g., an oligonucleotide comprising the nucleotidesequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked to a molecular payload, wherein the anti-TfRantibody comprises a VH comprising the amino acid sequence of SEQ ID NO:77 or SEQ ID NO: 79, and a VL comprising the amino acid sequence of SEQID NO: 80. In some embodiments, the molecular payload is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked to a molecular payload, wherein the anti-TfRantibody comprises a heavy chain comprising the amino acid sequence ofSEQ ID NO: 84, SEQ ID NO: 86 or SEQ ID NO: 87 and a light chaincomprising the amino acid sequence of SEQ ID NO: 85. In someembodiments, the molecular payload is a DUX4-targeting oligonucleotide(e.g., an oligonucleotide comprising the nucleotide sequence of SEQ IDNO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked to a molecular payload, wherein the anti-TfRantibody comprises a heavy chain comprising the amino acid sequence ofSEQ ID NO: 88 or SEQ ID NO: 91, and a light chain comprising the aminoacid sequence of SEQ ID NO: 89. In some embodiments, the molecularpayload is a DUX4-targeting oligonucleotide (e.g., an oligonucleotidecomprising the nucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked to a molecular payload, wherein the anti-TfRantibody comprises a heavy chain comprising the amino acid sequence ofSEQ ID NO: 88 or SEQ ID NO: 91, and a light chain comprising the aminoacid sequence of SEQ ID NO: 90. In some embodiments, the molecularpayload is a DUX4-targeting oligonucleotide (e.g., an oligonucleotidecomprising the nucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked to a molecular payload, wherein the anti-TfRantibody comprises a heavy chain comprising the amino acid sequence ofSEQ ID NO: 92 or SEQ ID NO: 94, and a light chain comprising the aminoacid sequence of SEQ ID NO: 95. In some embodiments, the molecularpayload is a DUX4-targeting oligonucleotide (e.g., an oligonucleotidecomprising the nucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked to a molecular payload, wherein the anti-TfRantibody comprises a heavy chain comprising the amino acid sequence ofSEQ ID NO: 92, and a light chain comprising the amino acid sequence ofSEQ ID NO: 93. In some embodiments, the molecular payload is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked to a molecular payload, wherein the anti-TfRantibody comprises a heavy chain comprising the amino acid sequence ofSEQ ID NO: 97, SEQ ID NO: 98, or SEQ ID NO: 99 and a VL comprising theamino acid sequence of SEQ ID NO: 85. In some embodiments, the molecularpayload is a DUX4-targeting oligonucleotide (e.g., an oligonucleotidecomprising the nucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked to a molecular payload, wherein the anti-TfRantibody comprises a heavy chain comprising the amino acid sequence ofSEQ ID NO: 100 or SEQ ID NO: 101 and a light chain comprising the aminoacid sequence of SEQ ID NO: 89. In some embodiments, the molecularpayload is a DUX4-targeting oligonucleotide (e.g., an oligonucleotidecomprising the nucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked to a molecular payload, wherein the anti-TfRantibody comprises a heavy chain comprising the amino acid sequence ofSEQ ID NO: 100 or SEQ ID NO: 101 and a light chain comprising the aminoacid sequence of SEQ ID NO: 90. In some embodiments, the molecularpayload is a DUX4-targeting oligonucleotide (e.g., an oligonucleotidecomprising the nucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked to a molecular payload, wherein the anti-TfRantibody comprises a heavy chain comprising the amino acid sequence ofSEQ ID NO: 102 and a light chain comprising the amino acid sequence ofSEQ ID NO: 93. In some embodiments, the molecular payload is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked to a molecular payload, wherein the anti-TfRantibody comprises a heavy chain comprising the amino acid sequence ofSEQ ID NO: 102 or SEQ ID NO: 103 and a light chain comprising the aminoacid sequence of SEQ ID NO: 95. In some embodiments, the molecularpayload is a DUX4-targeting oligonucleotide (e.g., an oligonucleotidecomprising the nucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked via a lysine to the 5′ end of anoligonucleotide, wherein the anti-TfR antibody comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 84 and a light chaincomprising the amino acid sequence of in SEQ ID NO: 85; wherein thecomplex has the structure of:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked via a lysine to the 5′ end of anoligonucleotide, wherein the anti-TfR antibody comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 86 and a light chaincomprising the amino acid sequence of in SEQ ID NO: 85; wherein thecomplex has the structure of:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked via a lysine to the 5′ end of anoligonucleotide, wherein the anti-TfR antibody comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 87 and a light chaincomprising the amino acid sequence of in SEQ ID NO: 85; wherein thecomplex has the structure of:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked via a lysine to the 5′ end of anoligonucleotide, wherein the anti-TfR antibody comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 88 and a light chaincomprising the amino acid sequence of in SEQ ID NO: 89; wherein thecomplex has the structure of:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked via a lysine to the 5′ end of anoligonucleotide, wherein the anti-TfR antibody comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 88 and a light chaincomprising the amino acid sequence of in SEQ ID NO: 90; wherein thecomplex has the structure of:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked via a lysine to the 5′ end of anoligonucleotide, wherein the anti-TfR antibody comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 91 and a light chaincomprising the amino acid sequence of in SEQ ID NO: 89; wherein thecomplex has the structure of:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked via a lysine to the 5′ end of anoligonucleotide, wherein the anti-TfR antibody comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 91 and a light chaincomprising the amino acid sequence of in SEQ ID NO: 90; wherein thecomplex has the structure of:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked via a lysine to the 5′ end of anoligonucleotide, wherein the anti-TfR antibody comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 92 and a light chaincomprising the amino acid sequence of in SEQ ID NO: 93; wherein thecomplex has the structure of:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked via a lysine to the 5′ end of anoligonucleotide, wherein the anti-TfR antibody comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 94 and a light chaincomprising the amino acid sequence of in SEQ ID NO: 95; wherein thecomplex has the structure of:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRantibody covalently linked via a lysine to the 5′ end of anoligonucleotide, wherein the anti-TfR antibody comprises a heavy chaincomprising the amino acid sequence of SEQ ID NO: 92 and a light chaincomprising the amino acid sequence of in SEQ ID NO: 95; wherein thecomplex has the structure of:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRFab covalently linked via a lysine to the 5′ end of an oligonucleotide,wherein the anti-TfR Fab comprises a VH comprising the amino acidsequence of SEQ ID NO: 69 and a VL comprising the amino acid sequence ofin SEQ ID NO: 70; wherein the complex has the structure of:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRFab covalently linked via a lysine to the 5′ end of an oligonucleotide,wherein the anti-TfR Fab comprises a VH comprising the amino acidsequence of SEQ ID NO: 71 and a VL comprising the amino acid sequence ofin SEQ ID NO: 70; wherein the complex has the structure of:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRFab covalently linked via a lysine to the 5′ end of an oligonucleotide,wherein the anti-TfR Fab comprises a VH comprising the amino acidsequence of SEQ ID NO: 72 and a VL comprising the amino acid sequence ofin SEQ ID NO: 70; wherein the complex has the structure of:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRFab covalently linked via a lysine to the 5′ end of an oligonucleotide,wherein the anti-TfR Fab comprises a VH comprising the amino acidsequence of SEQ ID NO: 73 and a VL comprising the amino acid sequence ofin SEQ ID NO: 74; wherein the complex has the structure of:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRFab covalently linked via a lysine to the 5′ end of an oligonucleotide,wherein the anti-TfR Fab comprises a VH comprising the amino acidsequence of SEQ ID NO: 73 and a VL comprising the amino acid sequence ofin SEQ ID NO: 75; wherein the complex has the structure of:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRFab covalently linked via a lysine to the 5′ end of an oligonucleotide,wherein the anti-TfR Fab comprises a VH comprising the amino acidsequence of SEQ ID NO: 76 and a VL comprising the amino acid sequence ofin SEO ID NO: 74; wherein the complex has the structure of:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRFab covalently linked via a lysine to the 5′ end of an oligonucleotide,wherein the anti-TfR Fab comprises a VH comprising the amino acidsequence of SEQ ID NO: 76 and a VL comprising the amino acid sequence ofin SEQ ID NO: 75; wherein the complex has the structure of:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRFab covalently linked via a lysine to the 5′ end of an oligonucleotide,wherein the anti-TfR Fab comprises a VH comprising the amino acidsequence of SEQ ID NO: 77 and a VL comprising the amino acid sequence ofin SEQ ID NO: 78; wherein the complex has the structure of:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRFab covalently linked via a lysine to the 5′ end of an oligonucleotide,wherein the anti-TfR Fab comprises a VH comprising the amino acidsequence of SEQ ID NO: 79 and a VL comprising the amino acid sequence ofin SEQ ID NO: 80; wherein the complex has the structure of:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRFab covalently linked via a lysine to the 5′ end of an oligonucleotide,wherein the anti-TfR Fab comprises a VH comprising the amino acidsequence of SEQ ID NO: 77 and a VL comprising the amino acid sequence ofin SEQ ID NO: 80; wherein the complex has the structure of:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRFab covalently linked via a lysine to the 5′ end of an oligonucleotide,wherein the anti-TfR Fab comprises a heavy chain comprising the aminoacid sequence of SEQ ID NO: 97 and a light chain comprising the aminoacid sequence of in SEQ ID NO: 85; wherein the complex has the structureof:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRFab covalently linked via a lysine to the 5′ end of an oligonucleotide,wherein the anti-TfR Fab comprises a heavy chain comprising the aminoacid sequence of SEQ ID NO: 98 and a light chain comprising the aminoacid sequence of in SEQ ID NO: 85; wherein the complex has the structureof:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRFab covalently linked via a lysine to the 5′ end of an oligonucleotide,wherein the anti-TfR Fab comprises a heavy chain comprising the aminoacid sequence of SEQ ID NO: 99 and a light chain comprising the aminoacid sequence of in SEQ ID NO: 85; wherein the complex has the structureof:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRFab covalently linked via a lysine to the 5′ end of an oligonucleotide,wherein the anti-TfR Fab comprises a heavy chain comprising the aminoacid sequence of SEQ ID NO: 100 and a light chain comprising the aminoacid sequence of in SEQ ID NO: 89; wherein the complex has the structureof:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRFab covalently linked via a lysine to the 5′ end of an oligonucleotide,wherein the anti-TfR Fab comprises a heavy chain comprising the aminoacid sequence of SEQ ID NO: 100 and a light chain comprising the aminoacid sequence of in SEQ ID NO: 90; wherein the complex has the structureof:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRFab covalently linked via a lysine to the 5′ end of an oligonucleotide,wherein the anti-TfR Fab comprises a heavy chain comprising the aminoacid sequence of SEQ ID NO: 101 and a light chain comprising the aminoacid sequence of in SEQ ID NO: 89; wherein the complex has the structureof:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO:151).

In some embodiments, the complex described herein comprises an anti-TfRFab covalently linked via a lysine to the 5′ end of an oligonucleotide,wherein the anti-TfR Fab comprises a heavy chain comprising the aminoacid sequence of SEQ ID NO: 101 and a light chain comprising the aminoacid sequence of in SEQ ID NO: 90; wherein the complex has the structureof:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRFab covalently linked via a lysine to the 5′ end of an oligonucleotide,wherein the anti-TfR Fab comprises a heavy chain comprising the aminoacid sequence of SEQ ID NO: 102 and a light chain comprising the aminoacid sequence of in SEQ ID NO: 93; wherein the complex has the structureof:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRFab covalently linked via a lysine to the 5′ end of an oligonucleotide,wherein the anti-TfR Fab comprises a heavy chain comprising the aminoacid sequence of SEQ ID NO: 103 and a light chain comprising the aminoacid sequence of in SEQ ID NO: 95; wherein the complex has the structureof:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, the complex described herein comprises an anti-TfRFab covalently linked via a lysine to the 5′ end of an oligonucleotide,wherein the anti-TfR Fab comprises a heavy chain comprising the aminoacid sequence of SEQ ID NO: 102 and a light chain comprising the aminoacid sequence of in SEQ ID NO: 95; wherein the complex has the structureof:

wherein n is 3 and m is 4. In some embodiments, the oligonucleotide is aDUX4-targeting oligonucleotide (e.g., an oligonucleotide comprising thenucleotide sequence of SEQ ID NO: 151).

In some embodiments, in any one of the examples of complexes describedherein, L1 is any one of the spacers described herein.

In some embodiments, L1 is:

wherein the piperazine moiety links to the oligonucleotide, wherein L2is

In some embodiments, L1 is:

wherein the piperazine moiety links to the oligonucleotide.

In some embodiments, L1 is

In some embodiments, L1 is linked to a 5′ phosphate of theoligonucleotide.

In some embodiments, L1 is optional (e.g., need not be present).

III. Formulations

Complexes provided herein may be formulated in any suitable manner.Generally, complexes provided herein are formulated in a manner suitablefor pharmaceutical use. For example, complexes can be delivered to asubject using a formulation that minimizes degradation, facilitatesdelivery and/or (e.g., and) uptake, or provides another beneficialproperty to the complexes in the formulation. In some embodiments,provided herein are compositions comprising complexes andpharmaceutically acceptable carriers. Such compositions can be suitablyformulated such that when administered to a subject, either into theimmediate environment of a target cell or systemically, a sufficientamount of the complexes enter target muscle cells. In some embodiments,complexes are formulated in buffer solutions such as phosphate-bufferedsaline solutions, liposomes, micellar structures, and capsids.

It should be appreciated that, in some embodiments, compositions mayinclude separately one or more components of complexes provided herein(e.g., muscle-targeting agents, linkers, molecular payloads, orprecursor molecules of any one of them).

In some embodiments, complexes are formulated in water or in an aqueoussolution (e.g., water with pH adjustments). In some embodiments,complexes are formulated in basic buffered aqueous solutions (e.g.,PBS). In some embodiments, formulations as disclosed herein comprise anexcipient. In some embodiments, an excipient confers to a compositionimproved stability, improved absorption, improved solubility and/or(e.g., and) therapeutic enhancement of the active ingredient. In someembodiments, an excipient is a buffering agent (e.g., sodium citrate,sodium phosphate, a tris base, or sodium hydroxide) or a vehicle (e.g.,a buffered solution, petrolatum, dimethyl sulfoxide, or mineral oil).

In some embodiments, a complex or component thereof (e.g.,oligonucleotide or antibody) is lyophilized for extending its shelf-lifeand then made into a solution before use (e.g., administration to asubject). Accordingly, an excipient in a composition comprising acomplex, or component thereof, described herein may be a lyoprotectant(e.g., mannitol, lactose, polyethylene glycol, or polyvinyl pyrolidone),or a collapse temperature modifier (e.g., dextran, ficoll, or gelatin).

In some embodiments, a pharmaceutical composition is formulated to becompatible with its intended route of administration. Examples of routesof administration include parenteral, e.g., intravenous, intradermal,subcutaneous, administration. Typically, the route of administration isintravenous or subcutaneous.

Pharmaceutical compositions suitable for injectable use include sterileaqueous solutions (where water soluble) or dispersions and sterilepowders for the extemporaneous preparation of sterile injectablesolutions or dispersions. The carrier can be a solvent or dispersionmedium containing, for example, water, ethanol, polyol (for example,glycerol, propylene glycol, and liquid polyethylene glycol, and thelike), and suitable mixtures thereof. In some embodiments, formulationsinclude isotonic agents, for example, sugars, polyalcohols such asmannitol, sorbitol, and sodium chloride in the composition. Sterileinjectable solutions can be prepared by incorporating the complexes in arequired amount in a selected solvent with one or a combination ofingredients enumerated above, as required, followed by filteredsterilization.

In some embodiments, a composition may contain at least about 0.1% ofthe complex, or component thereof, or more, although the percentage ofthe active ingredient(s) may be between about 1% and about 80% or moreof the weight or volume of the total composition. Factors such assolubility, bioavailability, biological half-life, route ofadministration, product shelf life, as well as other pharmacologicalconsiderations will be contemplated by one skilled in the art ofpreparing such pharmaceutical formulations, and as such, a variety ofdosages and treatment regimens may be desirable.

IV. Methods of Use/Treatment

Complexes comprising a muscle-targeting agent covalently linked to amolecular payload as described herein are effective in treating FSHD. Insome embodiments, complexes are effective in treating Type 1 FSHD. Insome embodiments, complexes are effective in treating Type 2 FSHD. Insome embodiments, FSHD is associated with deletions in D4Z4 repeatregions on chromosome 4 which contain the DUX4 gene. In someembodiments, FSHD is associated with mutations in the SMCHD1 gene.

In some embodiments, a subject may be a human subject, a non-humanprimate subject, a rodent subject, or any suitable mammalian subject. Insome embodiments, a subject may have myotonic dystrophy. In someembodiments, a subject has elevated expression of the DUX4 gene outsideof fetal development and the testes. In some embodiments, the subjecthas facioscapulohumeral muscular dystrophy of Type 1 or Type 2. In someembodiments, the subject having FSHD has mutations in the SMCHD1 gene.In some embodiments, the subject having FSHD has deletion mutations inD4Z4 repeat regions on chromosome 4.

An aspect of the disclosure includes methods involving administering toa subject an effective amount of a complex as described herein. In someembodiments, an effective amount of a pharmaceutical composition thatcomprises a complex comprising a muscle-targeting agent covalentlylinked to a molecular payload can be administered to a subject in needof treatment. In some embodiments, a pharmaceutical compositioncomprising a complex as described herein may be administered by asuitable route, which may include intravenous administration, e.g., as abolus or by continuous infusion over a period of time. In someembodiments, intravenous administration may be performed byintramuscular, intraperitoneal, intracerebrospinal, subcutaneous,intra-articular, intrasynovial, or intrathecal routes. In someembodiments, a pharmaceutical composition may be in solid form, aqueousform, or a liquid form. In some embodiments, an aqueous or liquid formmay be nebulized or lyophilized. In some embodiments, a nebulized orlyophilized form may be reconstituted with an aqueous or liquidsolution.

Compositions for intravenous administration may contain various carrierssuch as vegetable oils, dimethylactamide, dimethyformamide, ethyllactate, ethyl carbonate, isopropyl myristate, ethanol, and polyols(glycerol, propylene glycol, liquid polyethylene glycol, and the like).For intravenous injection, water soluble antibodies can be administeredby the drip method, whereby a pharmaceutical formulation containing theantibody and a physiologically acceptable excipients is infused.Physiologically acceptable excipients may include, for example, 5%dextrose, 0.9% saline, Ringer's solution or other suitable excipients.Intramuscular preparations, e.g., a sterile formulation of a suitablesoluble salt form of the antibody, can be dissolved and administered ina pharmaceutical excipient such as Water-for-Injection, 0.9% saline, or5% glucose solution.

In some embodiments, a pharmaceutical composition that comprises acomplex comprising a muscle-targeting agent covalently linked to amolecular payload is administered via site-specific or local deliverytechniques. Examples of these techniques include implantable depotsources of the complex, local delivery catheters, site specificcarriers, direct injection, or direct application.

In some embodiments, a pharmaceutical composition that comprises acomplex comprising a muscle-targeting agent covalently linked to amolecular payload is administered at an effective concentration thatconfers therapeutic effect on a subject. Effective amounts vary, asrecognized by those skilled in the art, depending on the severity of thedisease, unique characteristics of the subject being treated, e.g. age,physical conditions, health, or weight, the duration of the treatment,the nature of any concurrent therapies, the route of administration andrelated factors. These related factors are known to those in the art andmay be addressed with no more than routine experimentation. In someembodiments, an effective concentration is the maximum dose that isconsidered to be safe for the patient. In some embodiments, an effectiveconcentration will be the lowest possible concentration that providesmaximum efficacy.

Empirical considerations, e.g. the half-life of the complex in asubject, generally will contribute to determination of the concentrationof pharmaceutical composition that is used for treatment. The frequencyof administration may be empirically determined and adjusted to maximizethe efficacy of the treatment.

Generally, for administration of any of the complexes described herein,an initial candidate dosage may be about 1 to 100 mg/kg, or more,depending on the factors described above, e.g. safety or efficacy. Insome embodiments, a treatment will be administered once. In someembodiments, a treatment will be administered daily, biweekly, weekly,bimonthly, monthly, or at any time interval that provide maximumefficacy while minimizing safety risks to the subject. Generally, theefficacy and the treatment and safety risks may be monitored throughoutthe course of treatment.

The efficacy of treatment may be assessed using any suitable methods. Insome embodiments, the efficacy of treatment may be assessed byevaluation of observation of symptoms associated with FSHD includingmuscle mass loss and muscle atrophy, primarily in the muscles of theface, shoulder blades, and upper arms.

In some embodiments, a pharmaceutical composition that comprises acomplex comprising a muscle-targeting agent covalently linked to amolecular payload described herein is administered to a subject at aneffective concentration sufficient to inhibit activity or expression ofa target gene by at least 10%, at least 20%, at least 30%, at least 40%,at least 50%, at least 60%, at least 70%, at least 80%, at least 90% orat least 95% relative to a control, e.g. baseline level of geneexpression prior to treatment.

In some embodiments, a single dose or administration of a pharmaceuticalcomposition that comprises a complex comprising a muscle-targeting agentcovalently linked to a molecular payload described herein to a subjectis sufficient to inhibit activity or expression of a target gene for atleast 1-5, 1-10, 5-15, 10-20, 15-30, 20-40, 25-50, or more days. In someembodiments, a single dose or administration of a pharmaceuticalcomposition that comprises a complex comprising a muscle-targeting agentcovalently linked to a molecular payload described herein to a subjectis sufficient to inhibit activity or expression of a target gene for atleast 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12 weeks. In someembodiments, a single dose or administration of a pharmaceuticalcomposition that comprises a complex comprising a muscle-targeting agentcovalently linked to a molecular payload described herein to a subjectis sufficient to inhibit activity or expression of a target gene for atleast 1, 2, 3, 4, 5, or 6 months.

In some embodiments, a pharmaceutical composition may comprise more thanone complex comprising a muscle-targeting agent covalently linked to amolecular payload. In some embodiments, a pharmaceutical composition mayfurther comprise any other suitable therapeutic agent for treatment of asubject, e.g. a human subject having FSHD. In some embodiments, theother therapeutic agents may enhance or supplement the effectiveness ofthe complexes described herein. In some embodiments, the othertherapeutic agents may function to treat a different symptom or diseasethan the complexes described herein.

EXAMPLES Example 1: Targeting Gene Expression with Transfected AntisenseOligonucleotides

A siRNA that targets hypoxanthine phosphoribosyltransferase (HPRT) wastested in vitro for its ability to reduce expression levels of HPRT inan immortalized cell line. Briefly, Hepa 1-6 cells were transfected witheither a control siRNA (siCTRL; 100 nM) or the siRNA that targets HPRT(siHPRT; 100 nM), formulated with lipofectamine 2000. HPRT expressionlevels were evaluated 48 hours following transfection. A controlexperiment was also performed in which vehicle (phosphate-bufferedsaline) was delivered to Hepa 1-6 cells in culture and the cells weremaintained for 48 hours. As shown in FIG. 1 , it was found that the HPRTsiRNA reduced HPRT expression levels by about 90% compared withcontrols. Sequences of the siRNAs used are provided in Table 6.

TABLE 6 Sequences of siHPRT and siCTRL SEQ ID Sequence NO: siHPRT sense5′-UcCuAuGaCuGuAgAuUuUaU- 152 strand (CH₂)₆NH2-3′ siHPRT antisense5′-aUaAaAuCuAcAgUcAuAgGasAsu-3′ 153 strand siCTRL sense5′-UgUaAuAaCcAuAuCuAcCuU- 154 strand (CH₂)₆NH2-3′ siCTRL antisense5′-aAgGuAgAuAuGgUuAuUaCasAsa-3′ 155 strand Lower case - 2′-O-Meribonucleosides; Capital letter - 2′-Fluoro ribonucleosides; s -phosphorothioate linkage

Example 2: Targeting HPRT with a Muscle-Targeting Complex

A muscle-targeting complex was generated comprising the HPRT siRNA usedin Example 1 (siHPRT) covalently linked, via a non-cleavableN-gamma-maleimidobutyryl-oxysuccinimide ester (GMBS) linker, to RI7 217anti-TfR1 Fab (DTX-A-002), an anti-transferrin receptor antibody.

Briefly, the GMBS linker was dissolved in dry DMSO and coupled to the 3′end of the sense strand of siHPRT through amide bond formation underaqueous conditions. Completion of the reaction was verified by Kaisertest. Excess linker and organic solvents were removed by gel permeationchromatography. The purified, maleimide functionalized sense strand ofsiHPRT was then coupled to DTX-A-002 antibody using a Michael additionreaction.

The product of the antibody coupling reaction was then subjected to sizeexclusion chromatography (SEC) purification. antiTfR-siHPRT complexescomprising one or two siHPRT molecules covalently attached to DTX-A-002antibody were purified. Densitometry confirmed that the purified sampleof complexes had an average siHPRT to antibody ratio of 1.46. SDS-PAGEanalysis demonstrated that >90% of the purified sample of complexescomprised DTX-A-002 linked to either one or two siHPRT molecules.

Using the same methods as described above, a control IgG2a-siHPRTcomplex was generated comprising the HPRT siRNA used in Example 1(siHPRT) covalently linked via the GMBS linker to an IgG2a (Fab)antibody (DTX-A-003). Densitometry confirmed that DTX-C-001 (theIgG2a-siHPRT complex) had an average siHPRT to antibody ratio of 1.46and SDS-PAGE demonstrated that >90% of the purified sample of controlcomplexes comprised DTX-A-003 linked to either one or two siHPRTmolecules.

The antiTfR-siHPRT complex was then tested for cellular internalizationand inhibition of HPRT in cellulo. Hepa 1-6 cells, which have relativelyhigh expression levels of transferrin receptor, were incubated in thepresence of vehicle (phosphate-buffered saline), IgG2a-siHPRT (100 nM),antiTfR-siCTRL (100 nM), or antiTfR-siHPRT (100 nM), for 72 hours. Afterthe 72 hour incubation, the cells were isolated and assayed forexpression levels of HPRT (FIG. 2 ). Cells treated with theantiTfR-siHPRT demonstrated a reduction in HPRT expression by ˜50%relative to the cells treated with the vehicle control and to thosetreated with the IgG2a-siHPRT complex. Meanwhile, cells treated witheither of the IgG2a-siHPRT or antiTfR-siCTRL had HPRT expression levelscomparable to the vehicle control (no reduction in HPRT expression).These data indicate that the anti-transferrin receptor antibody of theantiTfR-siHPRT enabled cellular internalization of the complex, therebyallowing the siHPRT to inhibit expression of HPRT.

Example 3: Targeting HPRT in Mouse Muscle Tissues with aMuscle-Targeting Complex

The muscle-targeting complex described in Example 2, antiTfR-siHPRT, wastested for inhibition of HPRT in mouse tissues. C57BL/6 wild-type micewere intravenously injected with a single dose of a vehicle control(phosphate-buffered saline); siHPRT (2 mg/kg of siRNA); IgG2a-siHPRT (2mg/kg of siRNA, corresponding to 9 mg/kg antibody complex); orantiTfR-siHPRT (2 mg/kg of siRNA, corresponding to 9 mg/kg antibodycomplex). Each experimental condition was replicated in four individualC57BL/6 wild-type mice. Following a three-day period after injection,the mice were euthanized and segmented into isolated tissue types.Individual tissue samples were subsequently assayed for expressionlevels of HPRT (FIGS. 3A-3B and 4A-4E).

Mice treated with the antiTfR-siHPRT complex demonstrated a reduction inHPRT expression in gastrocnemius (31% reduction; p<0.05) and heart (30%reduction; p<0.05), relative to the mice treated with the siHPRT control(FIGS. 3A-3B). Meanwhile, mice treated with the IgG2a-siHPRT complex hadHPRT expression levels comparable to the siHPRT control (little or noreduction in HPRT expression) for all assayed muscle tissue types.

Mice treated with the antiTfR-siHPRT complex demonstrated no change inHPRT expression in non-muscle tissues such as brain, liver, lung,kidney, and spleen tissues (FIGS. 4A-4E).

These data indicate that the anti-transferrin receptor antibody of theantiTfR-siHPRT complex enabled cellular internalization of the complexinto muscle-specific tissues in an in vivo mouse model, thereby allowingthe siHPRT to inhibit expression of HPRT. These data further demonstratethat the antiTfR-oligonucleotide complexes of the current disclosure arecapable of specifically targeting muscle tissues.

Example 4: Targeting DUX4 with Transfected Antisense Oligonucleotides

Three DUX4-expressing cell lines (A549, U-2 OS, and HepG2 cell lines)and immortalized skeletal muscle myoblasts (SkMC) were screened forexpression of DUX4 mRNA (FIG. 5 ). Cells were seeded at a density of10,000 cells/well and harvested for total RNA. cDNA was synthesized fromthe total RNA extracts and qPCR was performed to determine concentrationof DUX4 relative to a control gene (PPIB) in technical quadruplicate.These data were used to aid in the selection of the U-2 OS cell line fordownstream development of DUX4-targeting oligonucleotides.

Following selection of U-2 OS cells for development of DUX4-targetingoligonucleotides, a phosphorodiamidate morpholino oligomer (PMO) versionof an antisense oligonucleotide that targets DUX4 (FM10 PMO) wasevaluated for its ability to target DUX4 in vitro. FM10 PMO comprisesthe sequence GGGCATTTTAATATATCTCTGAACT (SEQ ID NO: 151). A controlphosphorodiamidate morpholino oligomer (PMO), that comprises thesequence CCTCTTACCTCAGTTACAATTTATA (SEQ ID NO: 149), was utilized as anegative control.

Briefly, U-2 OS cells were seeded at a density of 10 k cells/well beforebeing allowed to recover overnight. Cells were then treated with eithera control PMO (10 μM) or with the FM10 PMO (10 μM). Cells were incubatedfor 72 hours before being harvested for total RNA. cDNA was thensynthesized from the total RNA extracts and qPCR was performed todetermine expression of downstream DUX4 genes (ZSCAN4, MBD3L2, TRIM43)in technical quadruplicate. All qPCR data were analyzed using a standardΔΔCT method and were normalized to a plate-based negative controlcomprised of untreated cells (i.e., without any oligonucleotide).Results were then converted to fold change to evaluate efficacy.

As shown in FIG. 6 , all of ZSCAN4, MBD3L2, and TRIM43 showed decreasedexpression in the presence of the FM10 PMO compared to the control PMO(42%, 34%, and 32%; respectively). These data demonstrate that the FM10PMO is capable of targeting DUX4 in vitro.

Example 5: Targeting DUX4 with a Muscle-Targeting Complex

A muscle-targeting complex is generated comprising an antisenseoligonucleotide that targets a mutant allele of DUX4 (DUX4 ASO)covalently linked, via a cathepsin cleavable linker, to DTX-A-002 (RI7217 (Fab)), an anti-transferrin receptor antibody.

Briefly, a maleimidocaproyl-L-valine-L-citrulline-p-aminobenzyl alcoholp-nitrophenyl carbonate (MC-Val-Cit-PABC-PNP) linker molecule is coupledto NH₂-C₆-DUX4 ASO using an amide coupling reaction. Excess linker andorganic solvents are removed by gel permeation chromatography. Thepurified Val-Cit-linker-DUX4 ASO is then coupled to a thiol on theanti-transferrin receptor antibody (DTX-A-002).

The product of the antibody coupling reaction is then subjected tohydrophobic interaction chromatography (HIC-HPLC) to purify themuscle-targeting complex. Densitometry and SDS-PAGE analysis of thepurified complex allow for determination of the average ratio ofASO-to-antibody and total purity, respectively.

Using the same methods as described above, a control complex isgenerated comprising DUX4 ASO covalently linked via a Val-Cit linker toan IgG2a (Fab) antibody.

The purified muscle-targeting complex comprising DTX-A-002 covalentlylinked to DUX4 ASO is then tested for cellular internalization andinhibition of DUX4. Disease-relevant muscle cells that have relativelyhigh expression levels of transferrin receptor, are incubated in thepresence of vehicle control (saline), muscle-targeting complex (100 nM),or control complex (100 nM) for 72 hours. After the 72 hour incubation,the cells are isolated and assayed for expression levels of DUX4.

Example 6: A Muscle-Targeting Complex Enables Cellular Internalizationand Targeting of DUX4

A muscle-targeting complex (anti-TfR antibody-FM10) was generatedcomprising the FM10 PMO covalently linked to an anti-transferrinreceptor antibody.

Briefly, purified Val-Cit-linker-FM10 was coupled to a functionalized15G11 antibody generated through modifying ε-amine on lysine of theantibody.

The product of the antibody coupling reaction was then purified.Ultrafiltration was then used to concentrate the conjugate anddensitometry confirmed that this sample of anti-TfR antibody-FM10complexes had an average ASO to antibody ratio of 1.9.

FM10 PMO comprises the sequence GGGCATTTTAATATATCTCTGAACT (SEQ ID NO:151).

Human U-2 OS cells were dosed with the complex. Briefly, U-2 OS cellswere seeded at a density of 10 k cells/well before being allowed torecover overnight. Cells were then treated with one of the followingtreatments—vehicle control (PBS), a siRNA that targets DUX4, naked FM10PMO (1 μM), naked FM10 PMO (10 μM), or anti-TfR antibody-FM10 (1 μM;equivalent to 800 nM naked PMO). Cells were incubated for 72 hoursbefore being harvested for total RNA. cDNA was then synthesized from thetotal RNA extracts and qPCR was performed to determine expression ofdownstream DUX4 genes (ZSCAN4, MBD3L2, TRIM43) in technicalquadruplicate. All qPCR data were analyzed using a standard MET methodand were normalized to a plate-based negative control comprised ofuntreated cells (i.e., without any oligonucleotide). Results were thenconverted to fold change to evaluate efficacy.

As shown in FIG. 7 , upregulation of DUX4 in FSHD leads to theupregulation of disease characteristic genes including ZSCAN4, MBD3L2,and TRIM43. In U-2 OS cells that express DUX4 and have elevated levelsof ZSCAN4, MDB3L2 and TRIM43, mirroring pathologically relevant eventsin FSHD patient cells, treatment with naked FM10 at 1 μM fails to reduceZSCAN4, MBD3L2, and TRIM43 expression. Increased concentration of nakedFM10 (to 10 μM) leads to a modest reduction in ZSCAN4 and TRIM43expression, but has no effect on MDB3L2 expression. In contrast,treatment with anti-TfR antibody-FM10 (1 μM concentration; equivalent to800 nM of naked FM10) significantly reduced expression of MBD3L2, ZSCAN4and TRIM43.

These data indicate that the anti-transferrin receptor antibody of theanti-TfR antibody-FM10 complex enabled cellular internalization of thecomplex into U-2 OS cells, thereby allowing the FM10 PMO to inhibitexpression of DUX4.

Example 7: Binding Affinity of Selected Anti-TfR1 Antibodies to HumanTfR1

Selected anti-TfR1 antibodies were tested for their binding affinity tohuman TfR1 for measurement of Ka (association rate constant), Kd(dissociation rate constant), and K_(D) (affinity). Two known anti-TfR1antibodies were used as control, 15G11 and OKT9. The binding experimentwas performed on Carterra LSA at 25° C. An anti-mouse IgG and anti-humanIgG antibody “lawn” was prepared on a HC30M chip by amine coupling. TheIgGs were captured on the chip. Dilution series of hTfR1, cyTfR1, andhTfR2 were injected to the chip for binding (starting from 1000 nM, 1:3dilution, 8 concentrations).

Binding data were referenced by subtracting the responses from a bufferanalyte injection and globally fitting to a 1:1 Langmuir binding modelfor estimate of Ka (association rate constant), Kd (dissociation rateconstant), and K_(D) (affinity) using the Carterra™ Kinetics software.5-6 concentrations were used for curve fitting.

The result showed that the mouse mAbs demonstrated binding to hTfR1 withK_(D) values ranging from 13 pM to 50 nM. A majority of the mouse mAbshad K_(D) values in the single digit nanomolar to sub-nanomolar range.The tested mouse mAbs showed cross-reactive binding to cyTfR1 with K_(D)values ranging from 16 pM to 22 nM.

Ka, Kd, and K_(D) values of anti-TfR1 antibodies are provided in Table10.

TABLE 10 Ka, Kd, and K_(D) values of anti-TfR1 antibodies Name K_(D) (M)Ka (M) Kd (M) ctrl-15G11 2.83E−10 3.70E+05 1.04E−04 ctrl-OKT9 mIgG5.36E−10 7.74E+05 4.15E−04 3-A04 4.36E−10 4.47E+05 1.95E−04 3-M127.68E−10 1.66E+05 1.27E−04 5-H12 2.08E−07 6.67E+04 1.39E−02

Example 8: Conjugation of Anti-TfR1 Antibodies with Oligonucleotides

Complexes containing an anti-TfR1 antibody covalently conjugated to atool oligo (ASO300) were generated. First, Fab fragments of anti-TfRantibody clones 3-A4, 3-M12, and 5-H12 were prepared by cutting themouse monoclonal antibodies with an enzyme in or below the hinge regionof the full IgG followed by partial reduction. The Fabs were confirmedto be comparable to mAbs in avidity or affinity.

Muscle-targeting complexes were generated by covalently linking theanti-TfR mAbs to the ASO300 via a cathepsin cleavable linker. Briefly, aBicyclo[6.1.0]nonyne-PEG3-L-valine-L-citrulline-pentafluorophenyl ester(BCN-PEG3-Val-Cit-PFP) linker molecule was coupled to ASO300 through acarbamate bond. Excess linker and organic solvents were removed bytangential flow filtration (TFF). The purified Val-Cit-linker-ASO wasthen coupled to an azide functionalized anti-transferrin receptorantibody generated through modifying ε-amine on lysine withAzide-PEG4-PFP. A positive control muscle-targeting complex was alsogenerated using 15G11.

The product of the antibody coupling reaction was then subjected to twopurification methods to remove free antibody and free payload.Concentrations of the conjugates were determined by either Nanodrop A280or BCA protein assay (for antibody) and Quant-It Ribogreen assay (forpayload). Corresponding drug-antibody ratios (DARs) were calculated.DARs ranged between 0.8 and 2.0, and were standardized so that allsamples receive equal amounts of payload.

The purified complexes were then tested for cellular internalization andinhibition of the target gene, DMPK. Non-human primate (NHP) or DM1(donated by DM1 patients) cells were grown in 96-well plates anddifferentiated into myotubes for 7 days. Cells were then treated withescalating concentrations (0.5 nM, 5 nM, 50 nM) of each complex for 72hours.

Cells were harvested, RNA was isolated, and reverse transcription wasperformed to generate cDNA. qPCR was performed using TaqMan kitsspecific for Ppib (control) and DMPK on the QuantStudio 7. The relativeamounts of remaining DMPK transcript in treated vs non-treated cellswere calculated and the results are shown in Table 11.

The results demonstrated that the anti-TfR1 antibodies are able totarget muscle cells, be internalized by the muscle cells with themolecular payload (the tool oligo ASO300), and that the molecularpayload (DMPK ASO) is able to target and knockdown the target gene(DMPK). Knockdown activity of a complex comprising the anti-TfR1antibody conjugated to a molecular payload (e.g., an oligonucleotide)targeting DUX4 can be tested in the same assay using an oligonucleotidetargeting DUX4 such as the FM10 oligonucleotide.

TABLE 11 Binding Affinity of anti-TfR1 Antibodies and Efficacy ofConjugates % knockdown of % knockdown of DMPK in cells huTfR1 cyTfR1DMPK in NHP from human DM1 Avg K_(D) Avg K_(D) cells using patientsusing (M) (M) Antibody-DMPK Antibody-DMPK Clone Name (antibody alone)(antibody alone) ASO conjugate ASO conjugate 15G11 (control)  8.0E−10 1.0E−09 36 46 3-A4 4.36E−10 2.32E−09 77 70 3-M12 7.68E−10 5.18E−09 7752 5-H12 2.02316E−07   1.20E−08 88 57

Interestingly, the DMPK knockdown results showed a lack of correlationbetween the binding affinity of the anti-TfR to transferrin receptor andefficacy in delivering a DMPK ASO to cells for DMPK knockdown.Surprisingly, the anti-TfR antibodies provided herein (e.g., at least3-A4, 3-M12, and 5-H12) demonstrated superior activity in delivering apayload (e.g., DMPK ASO) to the target cells and achieving thebiological effect of the molecular payload (e.g., DMPK knockdown) ineither cyno cells or human DM1 patient cells, compared to the controlantibody 15G11, despite the comparable binding affinity (or, in certaininstances, such as 5-H12, lower binding affinity) to human or cynotransferrin receptor between these antibodies and the control antibody15G11.

Top attributes such as high huTfR1 affinity, >50% knockdown of DMPK inNHP and DM1 patient cell line, identified epitope binding with 3 uniquesequences, low/no predicted PTM sites, and good expression andconjugation efficiency led to the selection of the top 3 clones forhumanization, 3-A4, 3-M12, and 5-H12.

Example 9: Humanized Anti-TfR1 Antibodies

The anti-TfR antibodies shown in Table 2 were subjected to humanizationand mutagenesis to reduce manufacturability liabilities. The humanizedvariants were screened and tested for their binding properties andbiological actives. Humanized variants of anti-TfR1 heavy and lightchain variable regions (5 variants each) were designed using CompositeHuman Technology. Genes encoding Fabs having these heavy and light chainvariable regions were synthesized, and vectors were constructed toexpress each humanized heavy and light chain variant. Subsequently, eachvector was expressed on a small scale and the resultant humanizedanti-TfR1 Fabs were analyzed. Humanized Fabs were selected for furthertesting based upon several criteria including Biocore assays of antibodyaffinity for the target antigen, relative expression, percent homologyto human germline sequence, and the number of MHC class II predicted Tcell epitopes (determined using iTope™ MCH class II in silico analysis).

Potential liabilities were identified within the parental sequence ofsome antibodies by introducing amino acid substitutions in the heavychain and light chain variable regions. These substitutions were chosenbased on relative expression levels, iTope™ score and relative K_(D)from Biacore single cycle kinetics analysis. The humanized variants weretested and variants were selected initially based upon affinity for thetarget antigen. Subsequently, the selected humanized Fabs were furtherscreened based on a series of biophysical assessments of stability andsusceptibility to aggregation and degradation of each analyzed variant,shown in Table 13 and Table 14. The selected Fabs were analyzed fortheir properties binding to TfR1 by kinetic analysis. The results ofthese analyses are shown in Table 7. For conjugates shown in Table 13and Table 14, the selected humanized Fabs were conjugated to aDMPK-targeting oligonucleotide AS0300. The selected Fabs are thermallystable, as indicated by the comparable binding affinity to human andcyno TfR1 after been exposed to high temperature (40° C.) for 9 days,compared to before the exposure (see Table 7).

TABLE 13 Biophysical assessment data for humanized anti-TfR Fabs Variant3M12 3M12 3M12 3M12 3A4 (VH3- Criteria (VH3/Vk2) (VH3/Vk3) (VH4/Vk2)(VH4/Vk3) N54T/Vk4) Binding Affinity 395 pM 345 pM 396 pM 341 pM 3.09 nM(Biacore d0) Binding Affinity 567 pM 515 pM 510 pM 486 pM 3.01 nM(Biacore d25) Fab binding 0.8 nM/ 0.6 nM/ 0.4 nM/ 0.5 nM/ 2.6 nM/affinity ELISA 9.9 nM 4.7 nM 1.4 nM 2.2 nM 156 nM* (human/cyno TfR1)Conjugate binding 2.2 nM/ N/A N/A 1.7 nM/ 2.8 nM/ affinity ELISA 2.9 nM2.1 nM 4.7 nM (human/cyno TfR1) . . . Variant 3A4 (VH3- 3A4 5H12 (VH5-5H12 (VH5- 5H12 (VH4- Criteria N54S/Vk4) (VH3/Vk4) C33Y/Vk3) C33D/Vk4)C33Y/Vk4) Binding Affinity 1.34 nM  1.5 nM  627 pM  991 pM  626 pM(Biacore d0) Binding Affinity 1.39 nM 1.35 nM 1.07 nM 3.01 nM 1.33 nM(Biacore d25) Fab binding 1.6 nM/ 1.5 nM/ 6.3 nM/ 6.0 nM/ 2.8 nM/affinity ELISA 398 nM* 122 nM* 2.1 nM 3.5 nM 3.3 nM (human/cyno TfR1)Conjugate binding 2.9 nM/ 2.8 nM/ 33.4 nM/ 110 nM/ 23.7 nM/ affinityELISA 7.8 nM 7.6 nM 2.3 nM 10.2 nM 3.3 nM (human/cyno TfR1) *Regainscyno binding after conjugation;

TABLE 14 Thermal Stability for humanized anti-TfR Fabs and conjugatesVariant 3M12 3M12 3M12 3M12 3A4 (VH3- Criteria (VH3/Vk2) (VH3/Vk3)(VH4/Vk2) (VH4/Vk3) N54T/Vk4) Binding affinity 0.8 0.6 0.4 0.5 2.6 hTfR1d0 (nM) Binding affinity 0.98 1.49 0.50 0.28 0.40 hTfR1 d9 (nM) Bindingaffinity 9.9 4.7 1.4 2.2 156 cyno TfR1 d0 (nM) Binding affinity 19.5115.58 5.01 16.40 127.50 cyno TfR1 d9 (nM) DMPK oligo 1.14 N/A N/A 1.182.22 conjugate binding to hTfR1 (nM) DMPK oligo 2.26 N/A N/A 1.85 5.12conjugate binding to cyno TfR1 (nM) . . . Variant 3A4 (VH3- 3A4 5H12(VH5- 5H12 (VH5- 5H12 (VH4- Criteria N54S/Vk4) (VH3/Vk4) C33Y/Vk3)C33D/Vk4) C33Y/Vk4) Binding affinity 1.6 1.5 6.3 6 2.8 hTfR1 d0 (nM)Binding affinity 0.65 0.46 71.90 92.34 1731.00 hTfR1 d9 (nM) Bindingaffinity 398 122 2.1 3.5 3.3 cyno TfR1 d0 (nM) Binding affinity 248.30878.40 0.69 0.63 0.26 cyno TfR1 d9 (nM) DMPK oligo 2.71 2.837 N/A 110.513.9 conjugate binding to hTfR1 (nM) DMPK oligo 4.1 7.594 N/A 10.18 13.9conjugate binding to cyno TfR1 (nM)

TABLE 7 Kinetic analysis of humanized anti-TfR Fabs binding to TfR1Humanized anti-TfR Fabs k_(a) (1/Ms) k_(d) (1/s) K_(D) (M) R_(MAX) Chi²(RU²) 3A4 (VH3/Vk4) 7.65E+10 1.15E+02 1.50E−09 48.0 0.776 3A4(VH3-N54S/Vk4) 4.90E+10 6.56E+01 1.34E−09 49.4 0.622 3A4 (VH3-N54T/Vk4)2.28E+05 7.05E−04 3.09E−09 61.1 1.650 3M12 (VH3/Vk2) 2.64E+05 1.04E−043.95E−10 78.4 0.037 3M12 (VH3/Vk3) 2.42E+05 8.34E−05 3.45E−10 91.1 0.0253M12 (VH4/Vk2) 2.52E+05 9.98E−05 3.96E−10 74.8 0.024 3M12 (VH4/Vk3)2.52E+05 8.61E−05 3.41E−10 82.4 0.030 5H12 (VH5-C33D/Vk4) 6.78E+056.72E−04 9.91E−10 49.3 0.093 5H12 (VH5-C33Y/Vk3) 1.95E+05 1.22E−046.27E−10 68.5 0.021 5H12 (VH5-C33Y/Vk4) 1.86E+05 1.17E−04 6.26E−10 75.20.026

Binding of Humanized Anti-TfR1 Fabs to TfR1 (ELISA)

To measure binding of humanized anti-TfR antibodies to TfR1, ELISAs wereconducted. High binding, black, flat bottom, 96 well plates (Corning#3925) were first coated with 100 μL/well of recombinant huTfR1 at 1μg/mL in PBS and incubated at 4° C. overnight. Wells were emptied andresidual liquid was removed. Blocking was conducted by adding 200 μL of1% BSA (w/w) in PBS to each well. Blocking was allowed to proceed for 2hours at room temperature on a shaker at 300 rpm. After blocking, liquidwas removed and wells were washed three times with 300 μL of TBST.Anti-TfR1 antibodies were then added in 0.5% BSA/TBST in triplicate inan 8 point serial dilution (dilution range 5 μg/mL-5 ng/mL). A positivecontrol and isotype controls were also included on the ELISA plate. Theplate was incubated at room temperature on an orbital shaker for 60minutes at 300 rpm, and the plate was washed three times with 300 μL ofTBST. Anti-(H+L)IgG-A488 (1:500) (Invitrogen #A11013) was diluted in0.5% BSA in TBST, and 100 μL was added to each well. The plate was thenallowed to incubate at room temperature for 60 minutes at 300 rpm onorbital shaker. The liquid was removed and the plate was washed fourtimes with 300 μL of TBST. Absorbance was then measured at 495 nmexcitation and 50 nm emission (with a 15 nm bandwidth) on a platereader. Data was recorded and analyzed for EC50. The data for binding tohuman TfR1 (hTfR1) for the humanized 3M12, 3A4 and 5H12 Fabs are shownin FIGS. 9A, 9C, and 9E, respectively. ELISA measurements were conductedusing cynomolgus monkey (Macaca fascicularis) TfR1 (cTfR1) according tothe same protocol described above for hTfR1, and results are shown inFIGS. 9B, 9D, and 9F.

Results of these two sets of ELISA analyses for binding of the humanizedanti-TfR Fabs to hTfR1 and cTfR1 demonstrate that humanized 3M12 Fabsshow consistent binding to both hTfR1 and cTfR1, and that humanized 3A4Fabs show decreased binding to cTfR1 relative to hTfR1.

Antibody-oligonucleotide conjugates were prepared using six humanizedanti-TfR Fabs, each of which were conjugated to a DMPK targetingoligonucleotide A50300. Conjugation efficiency and down-streampurification were characterized, and various properties of the productconjugates were measured. The results demonstrate that conjugationefficiency was robust across all 10 variants tested, and that thepurification process (hydrophobic interaction chromatography followed byhydroxyapatite resin chromatography) were effective. The purifiedconjugates showed a >97% purity as analyzed by size exclusionchromatography.

Several humanized Fabs were tested in cellular uptake experiments toevaluate TfR1-mediated internalization. To measure such cellular uptakemediated by antibodies, humanized anti-TfR Fab conjugates were labeledwith Cypher5e, a pH-sensitive dye. Rhabdomyosarcoma (RD) cells weretreated for 4 hours with 100 nM of the conjugates, trypsinized, washedtwice, and analyzed by flow cytometry. Mean Cypher5e fluorescence(representing uptake) was calculated using Attune NxT software. As shownin FIG. 10 , the humanized anti-TfR Fabs show similar or greaterendosomal uptake compared to a positive control anti-TfR1 Fab. Similarinternalization efficiencies were observed for different oligonucleotidepayloads. An anti-mouse TfR antibody was used as the negative control.Cold (non-internalizing) conditions abrogated the fluorescence signal ofthe positive control antibody-conjugate (data not shown), indicatingthat the positive signal in the positive control and humanized anti-TfRFab-conjugates is due to internalization of the Fab-conjugates.Similarly, oligonucleotides targeting DUX4 can also be conjugated to thehumanized anti-TfR Fabs and be internalized to muscle cells.

Conjugates of six humanized anti-TfR Fabs of were also tested forbinding to hTfR1 and cTfR1 by ELISA, and compared to the unconjugatedforms of the humanized Fabs. Results demonstrate that humanized 3M12 and5H12 Fabs maintain similar levels of hTfR1 and cTfR1 binding afterconjugation relative to their unconjugated forms (3M12, FIGS. 11A and11B; 5H12, FIGS. 11E and 11F). Interestingly, 3A4 clones show improvedbinding to cTfR1 after conjugation relative to their unconjugated forms(FIGS. 11C and 11D).

As used in this Example, the term ‘unconjugated’ indicates that theantibody was not conjugated to an oligonucleotide.

Example 10. Knockdown of DMPK mRNA Level Facilitated byAntibody-Oligonucleotide Conjugates In Vitro

Conjugates containing humanized anti-TfR Fabs 3M12(VH3/Vk2), 3M-12(VH4/Vk3), and 3A4(VH2-N54S/Vk4) were conjugated to a DMPK-targetingoligonucleotide AS0300 and were tested in rhabdomyosarcoma (RD) cellsfor knockdown of DMPK transcript expression. Antibodies were conjugatedto A50300 via the linker shown in Formula (C).

RD cells were cultured in a growth medium of DMEM with glutamine,supplemented with 10% FBS and penicillin/streptomycin until nearlyconfluent. Cells were then seeded into a 96 well plate at 20K cells perwell and were allowed to recover for 24 hours. Cells were then treatedwith the conjugates for 3 days. Total RNA was collected from cells, cDNAwas synthesized and DMPK expression was measured by qPCR.

Results in FIG. 12 show that DMPK expression level was reduced in cellstreated with each indicated conjugate, relative to expression inPBS-treated cells, indicating that the humanized anti-TfR Fabs are ableto mediate the uptake of the DMPK-targeting oligonucleotide by the RDcells and that the internalized DMPK-targeting oligonucleotide areeffective in knocking down DMPK mRNA level. Similarly, the humanizedanti-TfR Fabs can also facilitate the delivery of DUX4 targetingoligonucleotides to muscle cells for knocking down DUX4 expression.

Example 11. Functional Activity of Antibody-Conjugated OligonucleotidesTargeting DUX4 for Treating FSHD

FSHD patient-derived myotubes were treated with FM10 conjugated to ananti-TfR1 Fab or with naked FM10. FM10 has the sequence5′-GGGCATTTTAATATATCTCTGAACT-3′ (SEQ ID NO: 151). Expression of mRNAtranscribed from three genes known to be only expressed following DUX4activation was subsequently measured in the myotubes. Expression ofthese three DUX4-associated genes was reduced, as shown in FIG. 13A(naked oligonucleotide) and 13B (Ab-oligonucleotide). In addition, thehalf maximal concentration required to inhibit (IC₅₀) values for theconjugate were up to 9.6 times lower than those observed for nakedFM-10, as shown in Table 12 below, demonstrating that the conjugateswere up to 9.6 times more potent than naked FM10 in suppressingDUX4-associated gene expression.

Additional DUX4-targeting oligonucleotides that may also be used tosuppress DUX4-associated genes are ACUGCGCGCAGGUCUAGCCAGGAAG (SEQ ID NO:131) and UGCGCACUGCGCGCAGGUCUAGCCAGGAAG (SEQ ID NO: 156).

TABLE 12 IC₅₀ values for inhibition of DUX4-associated genes. Ab-FM-10Naked FM-10 Fold Improvement Transcript IC₅₀ (nM) IC₅₀ (nM) with Abconjugation ZSCAN4 67 643 9.6x MBD3L2 144 1208 8.4x TRIM43 352 1117 3.2x

Example 12. Serum Stability of the Linker Linking the Anti-TfR Antibodyand the Molecular Payload

Oligonucleotides which were linked to antibodies in examples wereconjugated via a cleavable linker shown in Formula (C). It is importantthat the linker maintain stability in serum and provide release kineticsthat favor sufficient payload accumulation in the targeted muscle cell.This serum stability is important for systemic intravenousadministration, stability of the conjugated oligonucleotide in thebloodstream, delivery to muscle tissue and internalization of thetherapeutic payload in the muscle cells. The linker has been confirmedto facilitate precise conjugation of multiple types of payloads(including ASOs, siRNAs and PMOs) to Fabs. This flexibility enabledrational selection of the appropriate type of payload to address thegenetic basis of each muscle disease. Additionally, the linker andconjugation chemistry allowed the optimization of the ratio of payloadmolecules attached to each Fab for each type of payload, and enabledrapid design, production and screening of molecules to enable use invarious muscle disease applications.

FIG. 8 shows serum stability of the linker in vivo, which was comparableacross multiple species over the course of 72 hours after intravenousdosing. At least 75% stability was measured in each case at 72 hoursafter dosing.

Example 13. Characterization of Binding Activities of Anti-TfR Fab 3M12VH4/Vk3

In vitro studies were performed to test the specificity of anti-TfR Fab3M12 VH4/Vk3 for human and cynomolgus monkey TfR1 binding and to confirmits selectivity for human TfR1 vs TfR2. The binding affinity of anti-TfRFab 3M12 VH4/Vk3 to TfR1 from various species was determined using anenzyme-linked immunosorbent assay (ELISA). Serial dilutions of the Fabwere added to plates precoated with recombinant human, cynomolgusmonkey, mouse, or rat TfR1. After a short incubation, binding of the Fabwas quantified by addition of a fluorescently tagged anti-(H+L) IgGsecondary antibody and measurement of fluorescence intensity at 495 nmexcitation and 520 nm emission. The Fab showed strong binding affinityto human and cynomolgus monkey TfR1, and no detectable binding of mouseor rat TfR1 was observed (FIG. 14 ). Surface plasmon resonance (SPR)measurements were also conducted, and results are shown in Table 15. TheKd of the Fab against the human TfR1 receptor was calculated to be7.68×10⁻¹⁰ M and against the cynomolgus monkey TfR1 receptor wascalculated to be 5.18×10⁻⁹M.

TABLE 15 Kinetic analysis of anti-TfR Fab 3M12 VH4/Vk3 binding to humanand cynomolgus monkey TfR1 or human TfR2, measured using surface plasmonresonance Anti-TfR Fab 3M12 VH4/Vk3 Target K_(d) (M) k_(a) (M⁻¹ s⁻¹)k_(d) (s⁻¹) R_(max) R_(es) SD Human 7.68E−10 1.66E+05 1.27E−04 1.11E+023.45E+00 TfR1 Cyno 5.18E−09 9.19E+04 4.76E−04 1.87E+02 6.24E+00 TfR1Human ND ND ND ND ND TfR2 ND = No detectable binding by SPR (10 pM-100uM)

To test for cross-reactivity of anti-TfR Fab 3M12 VH4/Vk3 to human TfR2,an ELISA was performed. Recombinant human TfR2 protein was platedovernight at 2 μg/mL and was blocked for 1 hour with 1% bovine serumalbumin (BSA) in PBS. Serial dilutions of the Fab or a positive controlanti-TfR2 antibody were added in 0.5% BSA/TBST for 1 hour. Afterwashing, anti-(H+L) IgG-A488 (Invitrogen #MA5-25932) fluorescentsecondary antibody was added at a 1:500 dilution in 0.5% BSA/TBST andthe plate was incubated for 1 hour. Relative fluorescence was measuredusing a Biotek Synergy plate reader at 495 nm excitation and 520 nmemission. No binding of anti-TfR Fab 3M12 VH4/Vk3 to hTfR2 was observed(FIG. 15 ).

Example 14. Serum Stability of Anti-TfR Fab-ASO Conjugate

Anti-TfR Fab VH4/Vk3 was conjugated to a control antisenseoligonucleotide (ASO) via a linker as shown in Formula (C) and theresulting conjugate was tested for stability of the linker conjugatingthe Fab to the ASO. Serum stability was measured by incubatingfluorescently labeled conjugate in PBS or in rat, mouse, cynomolgusmonkey, or human serum and measuring relative fluorescence intensityover time, with higher fluorescence indicating more conjugate remainingintact. FIG. 16 shows serum stability was similar across multiplespecies and remained high after 72 hours.

Example 15. Effects of Conjugates Containing an Anti-TfR Fab Conjugatedto a DUX4-Targeting Oligonucleotide in FSHD Patient-Derived ImmortalizedMyoblasts

An anti-TfR Fab 3M12 VH4/VK3 was conjugated to a DUX4-targetingoligonucleotide (SEQ ID NO: 151) via a cleavable Val-Cit linker toachieve enhanced muscle delivery of the oligonucleotide. Theoligonucleoside is a PMO and targets the polyadenylation signal of theDUX4 transcript. The activity of the conjugate was evaluated in theC6(AB1080) immortalized FSHD1 cell line, which has significant levels ofsurface TfR1 expression and activation of DUX4 transcriptome markers(MBD3L2, TRIM43, ZSCAN4). It is demonstrated that receptor-mediateddelivery of the PMO (SEQ ID NO: 151) by the anti-TfR Fab into musclecells resulted in ˜75% reduction of DUX4 transcriptome biomarkers at an8 nM PMO concentration, whereas equivalent unconjugated PMO shows nosignificant biomarker reduction compared to vehicle treated cells (FIG.17 ). The results show that conjugating with anti-TfR Fab enhancesdelivery of therapeutic oligonucleotides to muscle cells for thetreatment of FSHD.

As used in this Example, the term ‘unconjugated’ indicates that theoligonucleotide was not conjugated to an antibody.

Additionally, a dose response curve for reduction of MBD3L2 mRNA isshown in FIG. 18A. The half maximal concentration required to inhibit(IC50) value for the conjugate was 189 pM. Dose response curves forreduction of MBD3L2, TRIM43, and ZSCAN4 mRNA are shown in FIG. 18B. TheIC50 values for the conjugate inhibiting MBD3L2, TRIM43, and ZSCAN4 were200 pM, 50 pM, and 200 pM, respectively.

Experimental Procedures for Example 15 Cell Culture and Test ArticleTreatment

C6 (AB1080) immortalized FSHD myoblasts were seeded to a density of45,000 cells/well on a 96-well plate (ThermoFisher Scientific) inSkeletal Growth Media (CAT #C-23060, Promocell) with Supplementary mix(C-39365, Promocell) and 1% Penstrep (15140-122, Gibco). Growth mediawas replaced with differentiation media, NbActiv4 (Brainbits) and 1%Pen/Strep (Gibco), 24 hours later. The cells were treated withunconjugated DUX4-targeting oligonucleotide, the conjugate at a PMOconcentration of 8 nM, vehicle in technical replicates for 4 hours priorto washout with 1×PBS (10010023, Gibco) one time. Conditioneddifferentiation media was immediately added back to wells and the cellswere harvested 5 days later for downstream analyses.

For the dose response curves for MBD3L2, TRIM43, and ZSCAN4 knockdown,C6 (AB1080) immortalized FSHD myoblasts were treated as described abovebut with varying concentrations of the conjugates.

RNA Extraction and qPCR

Total RNA was extracted from cell monolayers with the RNeasy 96 Kit(Qiagen) in accordance with the manufacturer's instructions. The RNA wasquantified with the Biotek Plate Reader and diluted to 50 ng per samplewith Nuclease-Free Water (Qiagen) and reverse transcribed with qScriptcDNA SuperMix (QuantaBio). Gene expression was analyzed by qPCR withspecific TaqMan assays (ThermoFisher) by measuring levels of TRIM43(Hs00299174_m1), MBD3L2 (Hs00544743_m1), ZSCAN4 (Hs00537549_m1) andRPL13A (Hs04194366_g1) transcripts. Two-step amplification reactions andfluorescence measurements for Ct determination were conducted on aQuantStudio 7 instrument (Thermo Scientific). Log fold changes in theexpression of transcripts of interest were calculated according to the2-^(ΔΔCT) method using RPL13A as the reference gene and cells exposed tovehicle as the control group. Data are expressed as means±S.D.

Example 16. Pharmacokinetic Properties of Antibody-OligonucleotideConjugate in Non-Human Primates

A DUX4-targeting oligonucleotide (SEQ ID NO: 151) was administeredintravenously to non-human primates, either naked or conjugated to ananti-TfR1 antibody (3M12 VH4/Vk3 Fab). The naked oligonucleotide wasadministered at a dose of 30 mg/kg, and the conjugate was administeredat a dose of 3 mg/kg, 10 mg/kg, or 30 mg/kg oligonucleotide equivalent.Plasma levels of the oligonucleotide measured over time are shown inFIG. 19 . The results demonstrate that systemic exposure of theantibody-oligonucleotide conjugate shows dose-dependent pharmacokineticproperties, and achieves higher exposure relative to the nakedoligonucleotide. The plasma measurements also demonstrate theantibody-oligonucleotide conjugate has a long serum half-life of about60 hours. Furthermore, the antibody-oligonucleotide conjugatedemonstrates a 58-fold increase in area under the curve (AUC) and a3-fold increase in C_(max) compared to the naked oligonucleotide at anoligonucleotide equivalent dose of 30 mg/kg. These results aresummarized in Table 16.

TABLE 16 Pharmacokinetic values calculated from plasma concentrationmeasurements Antibody-Oligonucleotide Conjugate Oligonucleotide Dose(mg/kg) 3 10 30 30 C_(max) (μg/mL) 84 242 893 305 AUC_(t) (h*μg/mL) 9694714 15191 260 T_(1/2) (h) 61 58 56 N/A

Two-weeks following administration of the oligonucleotide or theantibody-oligonucleotied conjugate, necropsies were performed and muscletissues from the non-human primates were collected and oligonucleotidelevels were measured. In each muscle tissue tested (heart, orbiculariusoris, zygomatic major, diaphragm, trapezius, deltoid, gastrocnemius,biceps, quadriceps, and tibialis anterior), tissue oligonucleotidelevels were higher for each dose of antibody-oligonucleotide conjugate(3, 10, or 30 mg/kg oligonucleotide equivalent) compared to the nakedoligonucleotide (30 mg/kg) (FIG. 20 ). As a control, tissueoligonucleotide levels were also measured in tissues collected fromvehicle-treated animals, and no oligonucleotide was detected in any ofthe muscle tissues tested. These results demonstrate that theantibody-oligonucleotide conjugate achieves high exposure of theDUX4-targeting oligonucleotide to muscle tissue, and markedly higherthan oligonucleotide administered naked. At an oligonucleotideequivalent dose of 30 mg/kg, oligonucleotide concentrations in eachmuscle tested were 26- to 139-fold higher in animals treated withantibody-oligonucleotide conjugates relative to naked oligonucleotide.

To evaluate tissue accumulation of DUX4-targeting oligonucleotide overtime, tissue oligonucleotide levels were measured in gastrocnemiusbiopsy samples collected one-week following administration and comparedto the values measured in the necropsy samples collected two-weeksfollowing administration. The oligonucleotide levels were markedlyhigher in the gastrocnemius biopsy samples collected from the animalsadministered 3, 10, or 30 mg/kg oligonucleotide equivalent ofantibody-oligonucleotide conjugate than in the biopsy samples collectedfrom the animals administered 30 mg/kg naked oligonucleotide, and thelevels were even higher in the tissues collected two-weeks followingadministration (FIG. 21 ). No oligonucleotide was detected in tissuesamples from vehicle-treated animals. These results demonstrate that theantibody-oligonucleotide conjugate achieves high exposure of theDUX4-targeting oligonucleotide to muscle tissue when compared to nakedoligonucleotide, and that the conjugate continues to accumulate overtime.

Additional Embodiments

1. A complex comprising a muscle-targeting agent covalently linked to amolecular payload configured for inhibiting expression or activity ofDUX4, wherein the muscle-targeting agent specifically binds to aninternalizing cell surface receptor on muscle cells, wherein the muscletargeting agent is a humanized antibody that binds to a transferrinreceptor wherein the antibody comprises:

(i) a heavy chain variable region (VH) comprising an amino acid sequenceat least 85% identical to SEQ ID NO: 69; and/or a light chain variableregion (VL) comprising an amino acid sequence at least 85% identical toSEQ ID NO: 70;

(ii) a heavy chain variable region (VH) comprising an amino acidsequence at least 85% identical to SEQ ID NO: 71; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 85%identical to SEQ ID NO: 70;

(iii) a heavy chain variable region (VH) comprising an amino acidsequence at least 85% identical to SEQ ID NO: 72; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 85%identical to SEQ ID NO: 70;

(iv) a heavy chain variable region (VH) comprising an amino acidsequence at least 85% identical to SEQ ID NO: 73; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 85%identical to SEQ ID NO: 74;

(v) a heavy chain variable region (VH) comprising an amino acid sequenceat least 85% identical to SEQ ID NO: 73; and/or a light chain variableregion (VL) comprising an amino acid sequence at least 85% identical toSEQ ID NO: 75;

(vi) a heavy chain variable region (VH) comprising an amino acidsequence at least 85% identical to SEQ ID NO: 76; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 85%identical to SEQ ID NO: 74;

(vii) a heavy chain variable region (VH) comprising an amino acidsequence at least 85% identical to SEQ ID NO: 76; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 85%identical to SEQ ID NO: 75;

(viii) a heavy chain variable region (VH) comprising an amino acidsequence at least 85% identical to SEQ ID NO: 77; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 85%identical to SEQ ID NO: 78;

(ix) a heavy chain variable region (VH) comprising an amino acidsequence at least 85% identical to SEQ ID NO: 79; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 85%identical to SEQ ID NO: 80; or

(x) a heavy chain variable region (VH) comprising an amino acid sequenceat least 85% identical to SEQ ID NO: 77; and/or a light chain variableregion (VL) comprising an amino acid sequence at least 85% identical toSEQ ID NO: 80.

2. The complex of embodiment 1, wherein the antibody comprises:

(i) a VH comprising the amino acid sequence of SEQ ID NO: 69 and a VLcomprising the amino acid sequence of SEQ ID NO: 70;

(ii) a VH comprising the amino acid sequence of SEQ ID NO: 71 and a VLcomprising the amino acid sequence of SEQ ID NO: 70;

(iii) a VH comprising the amino acid sequence of SEQ ID NO: 72 and a VLcomprising the amino acid sequence of SEQ ID NO: 70;

(iv) a VH comprising the amino acid sequence of SEQ ID NO: 73 and a VLcomprising the amino acid sequence of SEQ ID NO: 74;

(v) a VH comprising the amino acid sequence of SEQ ID NO: 73 and a VLcomprising the amino acid sequence of SEQ ID NO: 75;

(vi) a VH comprising the amino acid sequence of SEQ ID NO: 76 and a VLcomprising the amino acid sequence of SEQ ID NO: 74;

(vii) a VH comprising the amino acid sequence of SEQ ID NO: 76 and a VLcomprising the amino acid sequence of SEQ ID NO: 75;

(viii) a VH comprising the amino acid sequence of SEQ ID NO: 77 and a VLcomprising the amino acid sequence of SEQ ID NO: 78;

(ix) a VH comprising the amino acid sequence of SEQ ID NO: 79 and a VLcomprising the amino acid sequence of SEQ ID NO: 80; or

(x) a VH comprising the amino acid sequence of SEQ ID NO: 77 and a VLcomprising the amino acid sequence of SEQ ID NO: 80.

3. The complex of embodiment 1 or embodiment 2, wherein the antibody isselected from the group consisting of a full-length IgG, a Fab fragment,a Fab′ fragment, a F(ab′)2 fragment, a scFv, and a Fv.

4. The complex of embodiment 3, wherein the antibody is a full-lengthIgG, optionally wherein the full-length IgG comprises a heavy chainconstant region of the isotype IgG1, IgG2, IgG3, or IgG4.

5. The complex of embodiment 4, wherein the antibody comprises:

(i) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 84; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 85;

(ii) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 86; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 85;

(iii) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 87; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 85;

(iv) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 88; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 89;

(v) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 88; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 90;

(vi) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 91; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 89;

(vii) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 91; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 90;

(viii) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 92; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 93;

(ix) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 94; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 95; or

(x) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 92; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 95.

6. The complex of embodiment 3, wherein the antibody is a Fab fragment.

7. The complex of embodiment 6, wherein the antibody comprises:

(i) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 97; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 85;

(ii) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 98; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 85;

(iii) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 99; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 85;

(iv) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 100; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 89;

(v) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 100; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 90;

(vi) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 101; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 89;

(vii) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 101; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 90;

(viii) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 102; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 93;

(ix) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 103; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 95; or

(x) a heavy chain comprising an amino acid sequence at least 85%identical to SEQ ID NO: 102; and/or a light chain comprising an aminoacid sequence at least 85% identical to SEQ ID NO: 95.

8. The complex of embodiment 6 or embodiment 7, wherein the antibodycomprises:

(i) a heavy chain comprising the amino acid sequence of SEQ ID NO: 97;and a light chain comprising the amino acid sequence of SEQ ID NO: 85;

(ii) a heavy chain comprising the amino acid sequence of SEQ ID NO: 98;and a light chain comprising the amino acid sequence of SEQ ID NO: 85;

(iii) a heavy chain comprising the amino acid sequence of SEQ ID NO: 99;and a light chain comprising the amino acid sequence of SEQ ID NO: 85;

(iv) a heavy chain comprising the amino acid sequence of SEQ ID NO: 100;and a light chain comprising the amino acid sequence of SEQ ID NO: 89;

(v) a heavy chain comprising the amino acid sequence of SEQ ID NO: 100;and a light chain comprising the amino acid sequence of SEQ ID NO: 90;

(vi) a heavy chain comprising the amino acid sequence of SEQ ID NO: 101;and a light chain comprising the amino acid sequence of SEQ ID NO: 89;

(vii) a heavy chain comprising the amino acid sequence of SEQ ID NO:101; and a light chain comprising the amino acid sequence of SEQ ID NO:90;

(viii) a heavy chain comprising the amino acid sequence of SEQ ID NO:102; and a light chain comprising the amino acid sequence of SEQ ID NO:93;

(ix) a heavy chain comprising the amino acid sequence of SEQ ID NO: 103;and a light chain comprising the amino acid sequence of SEQ ID NO: 95;or

(x) a heavy chain comprising the amino acid sequence of SEQ ID NO: 102;and a light chain comprising the amino acid sequence of SEQ ID NO: 95.

9. The complex of any one of embodiments 1 to 5, wherein the equilibriumdissociation constant (K_(D)) of binding of the antibody to thetransferrin receptor is in a range from 10⁻¹¹M to 10⁻⁶ M.

10. The complex of any one of embodiments 1 to 9, wherein the antibodydoes not specifically bind to the transferrin binding site of thetransferrin receptor and/or wherein the antibody does not inhibitbinding of transferrin to the transferrin receptor.

11. The complex of any one of embodiments 1 to 10, wherein the antibodyis cross-reactive with extracellular epitopes of two or more of a human,non-human primate and rodent transferrin receptor.

12. The complex of any one of embodiments 1 to 11, wherein the complexis configured to promote transferrin receptor mediated internalizationof the molecular payload into a muscle cell.

13. The complex of any one of embodiments 1 to 12, wherein the antibodyis a chimeric antibody, wherein optionally the chimeric antibody is ahumanized monoclonal antibody.

14. The complex of any one of embodiments 1 to 13, wherein the antibodyis in the form of a ScFv, Fab fragment, Fab′ fragment, F(ab′)2 fragment,or Fv fragment.

15. The complex of any one of embodiments 1 to 14, wherein the molecularpayload is an oligonucleotide.

16. The complex of embodiment 15, wherein the oligonucleotide comprisesat least 15 consecutive nucleotides of SEQ ID NO: 151(GGGCATTTTAATATATCTCTGAACT).

17. The complex of embodiment 16, wherein the oligonucleotide comprisesSEQ ID NO: 151 (GGGCATTTTAATATATCTCTGAACT).

18. The complex of any one of embodiments 15 to 17, wherein theoligonucleotide comprises a sequence that is complementary to at least15 consecutive nucleotides of SEQ ID NO: 150(AGTTCAGAGATATATTAAAATGCCC).

19. The complex of any one of embodiments 15 to 18, wherein theoligonucleotide comprises a region of complementarity to DUX4 gene.

20. The complex of any one of embodiments 1 to 14, wherein the molecularpayload is a polypeptide that inhibits DUX4 expression.

21. The complex of embodiment 20, wherein the polypeptide binds to aDUX4 enhancer sequence, thereby blocking recruitment of one or moreactivators of DUX4 expression.

22. The complex of any one of embodiments 15 to 19, wherein theoligonucleotide comprises an antisense strand that hybridizes, in acell, with a wild-type DUX4 mRNA transcript encoded by the allele.

23. The complex of any one of embodiments 15 to 19, wherein theoligonucleotide comprises an antisense strand that hybridizes, in acell, with a mutant DUX4 mRNA transcript encoded by the allele.

24. The complex of embodiment 23, wherein the oligonucleotide comprisesa strand complementary to the coding sequence of DUX4.

25. The complex of embodiment 23, wherein the oligonucleotide comprisesa strand complementary to the non-coding sequence of DUX4.

26. The complex of embodiment 25, wherein the oligonucleotide comprisesa strand complementary to a 5′ or 3′ UTR sequence of DUX4.

27. The complex of embodiment 23, wherein the oligonucleotide mediatesepigenetic silencing of DUX4.

28. The complex of any one of embodiments 15 to 19 or 22 to 27, whereinthe oligonucleotide comprises at least one modified internucleotidelinkage.

29. The complex of embodiment 28, wherein the at least one modifiedinternucleotide linkage is a phosphorothioate linkage.

30. The complex of embodiment 29, wherein the oligonucleotide comprisesphosphorothioate linkages in the Rp stereochemical conformation and/orin the Sp stereochemical conformation.

31. The complex of embodiment 30, wherein the oligonucleotide comprisesphosphorothioate linkages that are all in the Rp stereochemicalconformation or that are all in the Sp stereochemical conformation.

32. The complex of any one of embodiments 15 to 19 or 22 to 31, whereinthe oligonucleotide comprises one or more modified nucleotides.

33. The complex of embodiment 32, wherein the one or more modifiednucleotides are 2′-modified nucleotides.

34. The complex of any one of embodiments 15 to 19, or 22 to 33, whereinthe oligonucleotide is a gapmer oligonucleotide that directs RNAseH-mediated cleavage of the DUX4 mRNA transcript in a cell.

35. The complex of embodiment 34, wherein the gapmer oligonucleotidecomprises a central portion of 5 to 15 deoxyribonucleotides flanked bywings of 2 to 8 modified nucleotides. 36. The complex of embodiment 35,wherein the modified nucleotides of the wings are 2′-modifiednucleotides.

37. The complex of any one of embodiments 15 to 19 or 22 to 33, whereinthe oligonucleotide is a mixmer oligonucleotide.

38. The complex of embodiment 37, wherein the mixmer oligonucleotideinhibits translation of a DUX4 mRNA transcript.

39. The complex of embodiment 37 or 38, wherein the mixmeroligonucleotide comprises two or more different 2′ modified nucleotides.

40. The complex of any one of embodiments 15 to 19 or 22 to 33, whereinthe oligonucleotide is an RNAi oligonucleotide that promotesRNAi-mediated cleavage of the DUX4 mRNA transcript.

41. The complex of embodiment 40, wherein the RNAi oligonucleotide is adouble-stranded oligonucleotide of 19 to 25 nucleotides in length.

42. The complex of embodiment 40 or 41, wherein the RNAi oligonucleotidecomprises at least one 2′ modified nucleotide.

43. The complex of embodiment 33, 36, 39, or 42, wherein each 2′modified nucleotide is selected from the group consisting of:2′-O-methyl, 2′-fluoro (2′-F), 2′-O-methoxyethyl (2′-MOE), and 2′,4′-bridged nucleotides.

44. The complex of embodiment 32, wherein the one or more modifiednucleotides are bridged nucleotides.

45. The complex embodiment 33, 36, 39, or 42, wherein at least one 2′modified nucleotide is a 2′,4′-bridged nucleotide selected from:2′,4′-constrained 2′-O-ethyl (cEt) and locked nucleic acid (LNA)nucleotides.

46. The complex of any one of embodiments 15 to 19 or 22 to 33, whereinthe oligonucleotide comprises a guide sequence for a genome editingnuclease.

47. The complex of any one of embodiments 15 to 19 or 22 to 33, whereinthe oligonucleotide is a phosphorodiamidite morpholino oligomer.

48. The complex of any one of embodiments 1 to 47, wherein themuscle-targeting agent is covalently linked to the molecular payload viaa cleavable linker.

49. The complex of embodiment 48, wherein the cleavable linker isselected from: a protease-sensitive linker, pH-sensitive linker, andglutathione-sensitive linker.

50. The complex of embodiment 49, wherein the cleavable linker is aprotease-sensitive linker.

51. The complex of embodiment 50, wherein the protease-sensitive linkercomprises a sequence cleavable by a lysosomal protease and/or anendosomal protease.

52. The complex of embodiment 50, wherein the protease-sensitive linkercomprises a valine-citrulline dipeptide sequence.

53. The complex of embodiment 49, wherein the linker is pH-sensitivelinker that is cleaved at a pH in a range of 4 to 6.

54. The complex of any one of embodiments 1 to 47, wherein themuscle-targeting agent is covalently linked to the molecular payload viaa non-cleavable linker.

55. The complex of embodiment 54, wherein the non-cleavable linker is analkane linker.

56. The complex of any one of embodiments 1 to 55, wherein the antibodycomprises a non-natural amino acid to which the oligonucleotide iscovalently linked.

57. The complex of any one of embodiments 1 to 55, wherein the antibodyis covalently linked to the oligonucleotide via conjugation to a lysineresidue or a cysteine residue of the antibody.

58. The complex of embodiment 57, wherein the oligonucleotide isconjugated to the cysteine of the antibody via a maleimide-containinglinker, optionally wherein the maleimide-containing linker comprises amaleimidocaproyl or maleimidomethyl cyclohexane-1-carboxylate group.

59. The complex of embodiments 1 to 58, wherein the antibody is aglycosylated antibody that comprises at least one sugar moiety to whichthe oligonucleotide is covalently linked.

60. The complex of embodiment 59, wherein the sugar moiety is a branchedmannose.

61. The complex of embodiment 59 or 60, wherein the antibody is aglycosylated antibody that comprises one to four sugar moieties each ofwhich is covalently linked to a separate oligonucleotide.

62. The complex of embodiment 59, wherein the antibody is afully-glycosylated antibody.

63. The complex of embodiment 59, wherein the antibody is apartially-glycosylated antibody.

64. The complex of embodiment 63, wherein the partially-glycosylatedantibody is produced via chemical or enzymatic means.

65. The complex of embodiment 63, wherein the partially-glycosylatedantibody is produced in a cell that is deficient for an enzyme in the N-or O-glycosylation pathway.

66. A method of delivering a molecular payload to a cell expressingtransferrin receptor, the method comprising contacting the cell with thecomplex of any one of embodiments 1 to 65.

67. A method of inhibiting expression or activity of DUX4 in a cell, themethod comprising contacting the cell with the complex of any one ofembodiments 1 to 65 in an amount effective for promoting internalizationof the molecular payload to the cell.

68. The method of embodiment 67, wherein the cell is in vitro.

69. The method of embodiment 67, wherein the cell is in a subject.

70. The method of embodiment 69, wherein the subject is a human.

71. A method of treating a subject having one or more deletions of aD4Z4 repeat in chromosome 4 that is associated with facioscapulohumeralmuscular dystrophy, the method comprising administering to the subjectan effective amount of the complex of any one of embodiments 1 to 65.

72. The method of embodiment 71, wherein the subject has 10 or fewerD4Z4 repeats.

73. The method of embodiment 72, wherein the subject has 9, 8, 7, 6, 5,4, 3, 2, or 1 D4Z4 repeats.

74. The method of embodiment 72, wherein the subject has no D4Z4repeats.

75. A complex comprising an anti-transferrin receptor (TfR) antibodycovalently linked to a molecular payload configured for reducingexpression or activity of DUX4, wherein the antibody comprises:

(i) a heavy chain variable region (VH) comprising an amino acid sequenceat least 85% identical to SEQ ID NO: 76; and/or a light chain variableregion (VL) comprising an amino acid sequence at least 85% identical toSEQ ID NO: 75;

(ii) a heavy chain variable region (VH) comprising an amino acidsequence at least 85% identical to SEQ ID NO: 69; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 85%identical to SEQ ID NO: 70;

(iii) a heavy chain variable region (VH) comprising an amino acidsequence at least 85% identical to SEQ ID NO: 71; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 85%identical to SEQ ID NO: 70;

(iv) a heavy chain variable region (VH) comprising an amino acidsequence at least 85% identical to SEQ ID NO: 72; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 85%identical to SEQ ID NO: 70;

(v) a heavy chain variable region (VH) comprising an amino acid sequenceat least 85% identical to SEQ ID NO: 73; and/or a light chain variableregion (VL) comprising an amino acid sequence at least 85% identical toSEQ ID NO: 74;

(vi) a heavy chain variable region (VH) comprising an amino acidsequence at least 85% identical to SEQ ID NO: 73; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 85%identical to SEQ ID NO: 75;

(vii) a heavy chain variable region (VH) comprising an amino acidsequence at least 85% identical to SEQ ID NO: 76; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 85%identical to SEQ ID NO: 74;

(viii) a heavy chain variable region (VH) comprising an amino acidsequence at least 85% identical to SEQ ID NO: 77; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 85%identical to SEQ ID NO: 78;

(ix) a heavy chain variable region (VH) comprising an amino acidsequence at least 85% identical to SEQ ID NO: 79; and/or a light chainvariable region (VL) comprising an amino acid sequence at least 85%identical to SEQ ID NO: 80; or

(x) a heavy chain variable region (VH) comprising an amino acid sequenceat least 85% identical to SEQ ID NO: 77; and/or a light chain variableregion (VL) comprising an amino acid sequence at least 85% identical toSEQ ID NO: 80.

76. A complex comprising an anti-transferrin receptor (TfR) antibodycovalently linked to a molecular payload configured for reducingexpression or activity of DUX4, wherein the anti-TfR antibody hasundergone pyroglutamate formation resulting from a post-translationalmodification.

EQUIVALENTS AND TERMINOLOGY

The disclosure illustratively described herein suitably can be practicedin the absence of any element or elements, limitation or limitationsthat are not specifically disclosed herein. Thus, for example, in eachinstance herein any of the terms “comprising”, “consisting essentiallyof”, and “consisting of” may be replaced with either of the other twoterms. The terms and expressions which have been employed are used asterms of description and not of limitation, and there is no intentionthat in the use of such terms and expressions of excluding anyequivalents of the features shown and described or portions thereof, butit is recognized that various modifications are possible within thescope of the disclosure. Thus, it should be understood that although thepresent disclosure has been specifically disclosed by preferredembodiments, optional features, modification and variation of theconcepts herein disclosed may be resorted to by those skilled in theart, and that such modifications and variations are considered to bewithin the scope of this disclosure.

In addition, where features or aspects of the disclosure are describedin terms of Markush groups or other grouping of alternatives, thoseskilled in the art will recognize that the disclosure is also therebydescribed in terms of any individual member or subgroup of members ofthe Markush group or other group.

It should be appreciated that, in some embodiments, sequences presentedin the sequence listing may be referred to in describing the structureof an oligonucleotide or other nucleic acid. In such embodiments, theactual oligonucleotide or other nucleic acid may have one or morealternative nucleotides (e.g., an RNA counterpart of a DNA nucleotide ora DNA counterpart of an RNA nucleotide) and/or (e.g., and) one or moremodified nucleotides and/or (e.g., and) one or more modifiedinternucleotide linkages and/or (e.g., and) one or more othermodification compared with the specified sequence while retainingessentially same or similar complementary properties as the specifiedsequence.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Embodiments of this invention are described herein. Variations of thoseembodiments may become apparent to those of ordinary skill in the artupon reading the foregoing description.

The inventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.Those skilled in the art will recognize, or be able to ascertain usingno more than routine experimentation, many equivalents to the specificembodiments of the invention described herein. Such equivalents areintended to be encompassed by the following claims.

1.-27. (canceled)
 28. A composition comprising complexes comprising ananti-transferrin receptor antibody covalently linked to at least oneoligonucleotide, wherein the antibody is a Fab and comprises a heavychain comprising the amino acid sequence of SEQ ID NO: 101 and a lightchain comprising the amino acid sequence of SEQ ID NO: 90, and whereineach anti-TfR antibody of the complexes is on average covalently linkedto 1 to 3 oligonucleotides, and wherein the oligonucleotide targets aDUX4 RNA.
 29. The composition of claim 28, wherein the heavy chain ofthe antibody comprises an N-terminal pyroglutamate.
 30. The compositionof claim 28, wherein the equilibrium dissociation constant (K_(D)) ofbinding of the antibody to the transferrin receptor is in a range from10⁻¹¹M to 10⁻⁶ M.
 31. The composition of claim 28, wherein theoligonucleotide comprises a region of complementarity to SEQ ID NO: 158,wherein the wherein the region of complementarity is 12-35 nucleotidesin length.
 32. The composition of claim 28, wherein the oligonucleotideis 15-35 nucleotides in length.
 33. The composition of claim 28, whereinthe oligonucleotide is 20-30 nucleotides in length.
 34. The compositionof claim 28, wherein the oligonucleotide comprises the nucleotidesequence of SEQ ID NO: 151, wherein any one or more of the thymine bases(T's) in the oligonucleotide may optionally be a uracil base (U). 35.The complex of claim 28, wherein the oligonucleotide is single stranded.36. The complex of claim 28, wherein the oligonucleotide is doublestranded.
 37. The composition of claim 28, wherein the oligonucleotidecomprises one or more modified nucleosides.
 38. The composition of claim28, wherein the oligonucleotide is a phosphorodiamidate morpholinooligomer.
 39. The composition of claim 28, wherein the antibody and themolecular payload are covalently linked via a linker.
 40. Thecomposition of claim 39, wherein the linker comprises a cleavablelinker.
 41. The composition of claim 40, wherein the linker comprises avaline-citrulline sequence.
 42. The composition of claim 28, wherein thecomplex comprises a structure of:

wherein n is 3 and m is 4, wherein L1 comprises a spacer that is asubstituted or unsubstituted aliphatic, substituted or unsubstitutedheteroaliphatic, substituted or unsubstituted carbocyclylene,substituted or unsubstituted heterocyclylene, substituted orunsubstituted arylene, substituted or unsubstituted heteroarylene, —O—,—N(R^(A))—, —S—, —C(═O)—, —C(═O)O—, —C(═O)NR^(A)—, —NR^(A)C(═O)—,—NR^(A)C(═O)R^(A)—, —C(═O)R^(A)—, —NR^(A)C(═O)O—, —NR^(A)C(═O)N(R^(A))—,—OC(═O)—, —OC(═O)O—, —OC(═O)N(R^(A))—, —S(O)₂NR^(A)—, —NR^(A)S(O)₂—, ora combination thereof, wherein each R^(A) is independently hydrogen orsubstituted or unsubstituted alkyl.
 43. The composition of claim 42,wherein L1 comprises a structure of:

wherein the piperazine moiety links to the oligonucleotide, wherein L2comprises


44. The composition of claim 43, wherein L2 comprises


45. A method of reducing DUX4 expression in muscle cells of a subject,the method comprising administering to the subject the composition ofclaim
 28. 46. The method of claim 45, wherein the subject is human. 47.The method of claim 45, wherein the subject is a cynomolgus.
 48. Themethod of claim 45, wherein the subject has one or more deletions of aD4Z4 repeat in chromosome
 4. 49. The method of claim 45, wherein thecomplex is intravenously administered to the subject.
 50. The method ofclaim 45, wherein the subject has facioscapulohumeral muscular dystrophy(FSHD).
 51. The method of claim 45, wherein the heavy chain of theantibody comprises an N-terminal pyroglutamate.